| 1. |
- Feierabend, Maja, 1990, et al.
(författare)
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Optical fingerprint of non-covalently functionalized transition metal dichalcogenides
- 2017
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:38, s. Article no 384003 -
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Tidskriftsartikel (refereegranskat)abstract
- Atomically thin transition metal dichalcogenides (TMDs) hold promising potential forapplications in optoelectronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibit efficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combination with circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials, they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach, where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we apply the density matrix theory to investigate the potential of non-covalently functionalized monolayer TMDs. Considering exemplary molecules with a strong dipole moment, we predict spectral redshifts and the appearance of an additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular characteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs, leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipole moments open a channel for coherent intervalley coupling between the high-symmetry K and K' points which may create new possibilities for spin-valleytronics application.
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| 2. |
- Gryglas-Borysiewicz, Marta, et al.
(författare)
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Hydrostatic-pressure-induced changes of magnetic anisotropy in (Ga, Mn) As thin films
- 2017
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:11
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Tidskriftsartikel (refereegranskat)abstract
- The impact of hydrostatic pressure on magnetic anisotropy energies in (Ga, Mn) As thin films with in-plane and out-of-plane magnetic easy axes predefined by epitaxial strain was investigated. In both types of sample we observed a clear increase in both in-plane and out-of-plane anisotropy parameters with pressure. The out-of-plane anisotropy constant is well reproduced by the mean-field p-d Zener model; however, the changes in uniaxial anisotropy are much larger than expected in the Mn-Mn dimer scenario.
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| 3. |
- Hejral, Uta, et al.
(författare)
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High energy surface x-ray diffraction applied to model catalyst surfaces at work
- 2021
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 33:7, s. 73001-73001
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts are materials that accelerate the rate of a desired chemical reaction. As such, they constitute an integral part in many applications ranging from the production of fine chemicals in chemical industry to exhaust gas treatment in vehicles. Accordingly, it is of utmost economic interest to improve catalyst efficiency and performance, which requires an understanding of the interplay between the catalyst structure, the gas phase and the catalytic activity under realistic reaction conditions at ambient pressures and elevated temperatures. In recent years efforts have been made to increasingly develop techniques that allow for investigating model catalyst samples under conditions closer to those of real technical catalysts. One of these techniques is high energy surface x-ray diffraction (HESXRD), which uses x-rays with photon energies typically in the range of 70-80 keV. HESXRD allows a fast data collection of three dimensional reciprocal space for the structure determination of model catalyst samples under operando conditions and has since been used for the investigation of an increasing number of different model catalysts. In this article we will review general considerations of HESXRD including its working principle for different model catalyst samples and the experimental equipment required. An overview over HESXRD investigations performed in recent years will be given, and the advantages of HESXRD with respect to its application to different model catalyst samples will be presented. Moreover, the combination of HESXRD with other operando techniques such as in situ mass spectrometry, planar laser-induced fluorescence and surface optical reflectance will be discussed. The article will close with an outlook on future perspectives and applications of HESXRD.
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| 4. |
- Huang, S. W., et al.
(författare)
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Polaronic effect in the x-ray absorption spectra of La 1-x Ca x MnO 3 manganites
- 2019
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 31:19
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy (XAS) is performed to study changes in the electronic structures of colossal magnetoresistance (CMR) and charged ordered (CO) La1-x Ca x MnO3 manganites with respect to temperature. The pre-edge features in O and Mn K-edge XAS spectra, which are highly sensitive to the local distortion of MnO6 octahedral, exhibit contrasting temperature dependence between CMR and CO samples. The seemingly counter-intuitive XAS temperature dependence can be reconciled in the context of polarons. These results help identify the most relevant orbital states associated with polarons and highlight the crucial role played by polarons in understanding the electronic structures of manganites.
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| 5. |
- Johansson, Niclas, et al.
(författare)
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Ambient pressure phase transitions over Ir(1 1 1): at the onset of CO oxidation
- 2017
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 29:44
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report on the adsorbate structures on an Ir(1 1 1) surface during the phase transition from the inactive to the active state during CO oxidation. The CO oxidation over Pt(1 1 1) is used as a reference case. Where Pt(1 1 1) either is inactive and CO covered or active and O covered, Ir(1 1 1) exhibits a transition state with co-existing chemisorbed O and CO. The observed structural differences are explained in terms of DFT-calculated adsorption energies. For Pt(1 1 1) the repulsive CO–O interaction makes co-existing chemisorbed CO and O unfavourable, while for Ir(1 1 1) the stronger O and CO adsorption allows for overcoming the repulsive interaction. At the onset of CO oxidation over Ir(1 1 1), a CO structure containing defects forms, which enables O2 to dissociatively adsorb on the Ir(1 1 1) surface, thus enabling the CO oxidation reaction. At the mass transfer limit, the Ir(1 1 1) surface is covered by a chemisorbed O structure with defects; hence, the active surface is predominately chemisorbed O covered at a total pressure of 0.5 mbar and no oxide formation is observed.
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| 6. |
- Johansson, Niclas, et al.
(författare)
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Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure
- 2017
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 29:44
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the reaction of phenylacetylene (PA) with chloro-, bromo-, and iodobenzene on the Au(1 1 1) surface as a model system for the gold-catalysed Sonogashira cross-coupling. Both ultrahigh vacuum-based and ambient pressure x-ray photoelectron spectroscopy show that iodo- and chlorobenzene (IB and CB) undergo the cross-coupling reaction towards diphenylacetylene. Bromobenzene (BB), in contrast, does not react in the UHV experiments. Further, at ambient pressure signs are found for poisoning of the Au(1 1 1) surface by a carbon species formed in the reaction. The understanding obtained in the reaction experiments are based on a thorough investigation of the adsorption of PA, IB, CB, and BB on the Au(1 1 1) surface by soft x-ray absorption spectroscopy and temperature-dependent x-ray photoelectron spectroscopy. In particular, the experiments provide the orientation of the intact adsorbates with respect to the surfaces at liquid nitrogen temperature. Dissociation in the temperature regime between −80 and −15 °C is observed for iodo- and chlorobenzene, but not for BB, in agreement with that only IB and CB, but not BB, react with PA to form diphenylacetylene. The difference is tentatively attributed to a difference in surface orientation of the different halobenzenes.
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| 7. |
- John Mukkattukavil, Deepak, et al.
(författare)
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Resonant inelastic soft x-ray scattering on LaPt2Si2
- 2022
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 34:32, s. 324003-
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2 single crystal at the Si 2p and La 4d edges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Si s and d local partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4f excitations. Calculations show that Pt d-LPDOS dominates the occupied states, and a sharp localized La f state is found in the unoccupied states, in line with the observations.
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| 8. |
- Lu, Hongduo, et al.
(författare)
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Ionic liquid interface at an electrode: Simulations of electrochemical properties using an asymmetric restricted primitive model
- 2018
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- © 2018 IOP Publishing Ltd. We use Monte Carlo simulations of a coarse-grained model to investigate structure and electrochemical behaviours at an electrode immersed in room temperature ionic liquids (RTILs). The simple RTIL model, which we denote the asymmetric restricted primitive model (ARPM), is composed of monovalent hard-sphere ions, all of the same size, in which the charge is asymmetrically placed. Not only the hard-sphere size (d), but also the charge displacement (b), is identical for all species, i.e. the monovalent RTIL ions are fully described by only two parameters (d, b). In earlier work, it was demonstrated that the ARPM can capture typical static RTIL properties in bulk solutions with remarkable accuracy. Here, we investigate its behaviour at an electrode surface. The electrode is assumed to be a perfect conductor and image charge methods are utilized to handle polarization effects. We find that the ARPM of the ionic liquid reproduces typical (static) electrochemical properties of RTILs. Our model predicts a declining differential capacitance with increasing temperature, which is expected from simple physical arguments. We also compare our ARPM, with the corresponding RPM description, at an elevated temperature (1000 K). We conclude that, even though ion pairing occurs in the ARPM system, reducing the concentration of 'free' ions, it is still better able to screen charge than a corresponding RPM melt. Finally, we evaluate the option to coarse-grain the model even further, by treating the fraction of the ions that form ion pairs implicitly, only through the contribution to the dielectric constant of the corresponding dipolar (ion pair) fluid. We conclude that this primitive representation of ion pairing is not able to reproduce the structures and differential capacitances of the system with explicit ion pairs. The main problem seems to be due to a limited dielectric screening in a layer near the electrode surface, resulting from a combination of orientational restrictions and a depleted dipole density.
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| 9. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Multi-scale approach for strain-engineering of phosphorene
- 2017
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:18, s. Article nr 185702 -
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Tidskriftsartikel (refereegranskat)abstract
- A multi-scale approach for the theoretical description of deformed phosphorene is presented. This approach combines a valence-force model to relate macroscopic strain to microscopic displacements of atoms and a tight-binding model with distance-dependent hopping parameters to obtain electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modeling of phosphorene devices. We demonstrate this for the case of inhomogeneously deformed phosphorene drum, which may be used as an exciton funnel.
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| 10. |
- Roosen-Runge, Felix, et al.
(författare)
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Self-diffusion of nonspherical particles fundamentally conflicts with effective sphere models
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:15
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Tidskriftsartikel (refereegranskat)abstract
- Modeling diffusion of nonspherical particles presents an unsolved and considerable challenge, despite its importance for the understanding of crowding effects in biology, food technology and formulation science. A common approach in experiment and simulation is to map nonspherical objects on effective spheres to subsequently use the established predictions for spheres to approximate phenomena for nonspherical particles. Using numerical evaluation of the hydrodynamic mobility tensor, we show that this so-called effective sphere model fundamentally fails to represent the self-diffusion in solutions of ellipsoids as well as rod-like assemblies of spherical beads. The effective sphere model drastically overestimates the slowing down of self-diffusion down to volume fractions below 0.01. Furthermore, even the linear term relevant at lower volume fraction is inaccurate, linked to a fundamental misconception of effective sphere models. To overcome the severe problems related with the use of effective sphere models, we suggest a protocol to predict the short-time self-diffusion of rod-like systems, based on simulations with hydrodynamic interactions that become feasible even for more complex molecules as the essential observable shows a negligible system-size effect.
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| 11. |
- Östman, Erik, et al.
(författare)
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Ising-like behaviour of mesoscopic magnetic chains
- 2018
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:36
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an experimental realization of the short range magnetic order in a one-dimensional Ising chain using fabricated mesospins. We confirm an excellent agreement between the experimental findings and simulations obtained using the original Ising model. In particular, we are able to show that the thermal behaviour of the mesoscopic Ising chain dominates over the thermal behaviour of the individual mesospins themselves, confirming that fabricated mesospins can be viewed as artificial magnetic atoms.
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| 12. |
- Jena, Suchit Kumar, et al.
(författare)
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Slow spin dynamics of cluster spin-glass spinel Zn(Fe1-xRu (x))(2)O-4 : role of Jahn-Teller active spin-1/2 Cu2+ ions at B-sites
- 2022
-
Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:40
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Tidskriftsartikel (refereegranskat)abstract
- We report the slow spin dynamics of cluster spin-glass (SG) spinel Zn(Fe1-xRux)(2)O-4 by means of detailed dc-magnetization and ac-susceptibility studies combined with the heat capacity analysis. Two specific compositions (x= 0.5, 0.75) have been investigated in detail along with the substitution of Jahn-Teller (JT) active spin-1/2 Cu2+ ions at B-sites. Measurements based on the frequency and temperature dependence of ac-susceptibility (chi(ac)(f, T)) and the subsequent analysis using the empirical scaling laws such as: (a) Vogel-Fulcher law and (b) Power law reveal the presence of cluster SG state below the characteristic freezing temperature T-SG (17.77 K (x= 0.5) and 14 K (x= 0.75)). Relaxation dynamics of both the compositions follow the non-mean field de Almeida-Thouless (AT)-line approach (T-SG(H) = T-SG(0)(1 - AH(2/phi))), with an ideal value of phi = 3. Nevertheless, the analysis of temperature dependent high field dc-susceptibility, chi(hf) (2 kOe <= H-DC <= 20 kOe, T) provides evidence for Gabay-Toulouse type mixed-phase (coexistence of SG and ferrimagnetic (FiM)) behaviour. Further, in the case of Cu0.2Zn0.8FeRuO4 system, slowly fluctuating magnetic clusters persist even above the short-range FiM ordering temperature (T-FiM) and their volume fraction vanishes completely across similar to 6T(FiM). This particular feature of the dynamics has been very well supported by the time decay of the thermoremanent magnetization and heat-capacity studies. We employed the high temperature series expansion technique to determine the symmetric exchange coupling (J(S)) between the spins which yields J(S) = -3.02 x 10(-5) eV for Cu0.2Zn0.8FeRuO4 representing the dominant intra-sublattice ferromagnetic interactions due to the dilute incorporation of the JT active Cu2+ ions. However, the antiferromagnetic coupling is predominant in ZnFeRuO4 and Cu0.2Zn0.8Fe0.5Ru1.5O4 systems. Finally, we deduced the magnetic phase diagram in the H-DC - T plane using the characteristic parameters obtained from the field variations of both ac- and dc-magnetization measurements.
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| 13. |
- Abergel, David S. L.
(författare)
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Robustness of topologically protected transport in graphene-boron nitride lateral heterostructures
- 2017
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:7
-
Tidskriftsartikel (refereegranskat)abstract
- Previously, graphene nanoribbons set in lateral heterostructures with hexagonal boron nitride were predicted to support topologically protected states at low energy. We investigate how robust the transport properties of these states are against lattice disorder. We find that forms of disorder that do not couple the two valleys of the zigzag graphene nanoribbon do not impact the transport properties at low bias, indicating that these lateral heterostructures are very promising candidates for chip-scale conducting interconnects. Forms of disorder that do couple the two valleys, such as vacancies in the graphene ribbon, or substantial inclusions of armchair edges at the graphene-hexagonal boron nitride interface will negatively affect the transport. However, these forms of disorder are not commonly seen in current experiments.
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| 14. |
- Adlmann, Franz, et al.
(författare)
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Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces : a statistical analysis of the scattering contributions
- 2018
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.
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| 15. |
- Alekhin, A., et al.
(författare)
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Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
- 2019
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 31:12
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs(-1) (close to the Fermi velocity) and the decay length on the order of 100nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.
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| 16. |
- Autieri, Carmine, et al.
(författare)
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A systematic study of 4d and 5d transition metal mediated exchange coupling between Fe and Gd nanolaminates
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:46
-
Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of the magnetic coupling between iron and gadolinium layers intermediated by 4d and 5d transition metals using density functional theory. We demonstrate that it is possible to find a magnetic coupling for most of them. In particular, for the early transition metals (d(1), d(2), d(3) and d(4)), a ferromagnetic coupling occurs even stronger than the 3d interlayers. Atomic size and the electronic configuration of the transition metals are crucial for the nature of the coupling. All the open shell transition metals present induced magnetic moments. By increasing the number of interlayers, an oscillating behavior in the magnetic coupling was found and the magnetic coupling goes to zero beyond four spacer layers. Using Monte Carlo simulations, we demonstrate that the interlayer strongly enhances the critical temperature in the Gd layers closest to the interface.
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| 17. |
- Aydin, Alhun, et al.
(författare)
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Quantum shape oscillations in the thermodynamic properties of confined electrons in core–shell nanostructures
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:2
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum shape effect appears under the size-invariant shape transformations of stronglyconfined structures. Such a transformation distinctively influences the thermodynamicproperties of confined particles. Due to their characteristic geometry, core–shellnanostructures are good candidates for quantum shape effects to be observed. Here weinvestigate the thermodynamic properties of non-interacting degenerate electrons confined incore–shell nanowires consisting of an insulating core and a GaAs semiconducting shell. Wederive the expressions of shape-dependent thermodynamic quantities and show the existenceof a new type of quantum oscillations due to shape dependence, in chemical potential, internalenergy, entropy and specific heat of confined electrons.We provide physical understanding ofour results by invoking the quantum boundary layer concept and evaluating the distributions ofquantized energy levels on Fermi function and in state space. Besides the density, temperatureand size, the shape per se also becomes a control parameter on the Fermi energy of confinedelectrons, which provides a new mechanism for fine tuning the Fermi level and changing thepolarity of semiconductors.
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| 18. |
- Aydin, Alhun, et al.
(författare)
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Thermodefect voltage in graphene nanoribbon junctions
- 2022
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:19
-
Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric junctions are often made of components of different materials characterized by distinct transport properties. Single material junctions, with the same type of charge carriers, have also been considered to investigate various classical and quantum effects on the thermoelectric properties of nanostructured materials. We here introduce the concept of defect-induced thermoelectric voltage, namely, thermodefect voltage, in graphene nanoribbon (GNR) junctions under a temperature gradient. Our thermodefect junction is formed by two GNRs with identical properties except the existence of defects in one of the nanoribbons. At room temperature the thermodefect voltage is highly sensitive to the types of defects, their locations, as well as the width and edge configurations of the GNRs. We computationally demonstrate that the thermodefect voltage can be as high as 1.7 mV K-1 for 555-777 defects in semiconducting armchair GNRs. We further investigate the Seebeck coefficient, electrical conductance, and electronic thermal conductance, and also the power factor of the individual junction components to explain the thermodefect effect. Taken together, our study presents a new pathway to enhance the thermoelectric properties of nanomaterials.
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| 19. |
- Bafekry, A., et al.
(författare)
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Biphenylene monolayer as a two-dimensional nonbenzenoid carbon allotrope: a first-principles study
- 2022
-
Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:1
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Tidskriftsartikel (refereegranskat)abstract
- In a very recent accomplishment, the two-dimensional form of biphenylene network (BPN) has been fabricated. Motivated by this exciting experimental result on 2D layered BPN structure, herein we perform detailed density-functional theory-based first-principles calculations, in order to gain insight into the structural, mechanical, electronic and optical properties of this promising nanomaterial. Our theoretical results reveal the BPN structure is constructed from three rings of tetragon, hexagon and octagon, meanwhile the electron localization function shows very strong bonds between the C atoms in the structure. The dynamical stability of BPN is verified via the phonon band dispersion calculations. The mechanical properties reveal the brittle behavior of BPN monolayer. The Youngs modulus has been computed as 0.1 TPa, which is smaller than the corresponding value of graphene, while the Poissons ratio determined to be 0.26 is larger than that of graphene. The band structure is evaluated to show the electronic features of the material; determining the BPN monolayer as metallic with a band gap of zero. The optical properties (real and imaginary parts of the dielectric function, and the absorption spectrum) uncover BPN as an insulator along the zz direction, while owning metallic properties in xx and yy directions. We anticipate that our discoveries will pave the way to the successful implementation of this 2D allotrope of carbon in advanced nanoelectronics.
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| 20. |
- Bafekry, A., et al.
(författare)
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Investigation of vacancy defects and substitutional doping in AlSb monolayer with double layer honeycomb structure: a first-principles calculation
- 2022
-
Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:6
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Tidskriftsartikel (refereegranskat)abstract
- The experimental knowledge of the AlSb monolayer with double layer honeycomb structure is largely based on the recent publication (Le Qin et al 2021 ACS Nano 15 8184), where this monolayer was recently synthesized. Therefore, the aim of our research is to consequently explore the effects of substitutional doping and vacancy point defects on the electronic and magnetic properties of the novel hexagonal AlSb monolayer. Besides experimental reports, the phonon band structure and cohesive energy calculations confirm the stability of the AlSb monolayer. Its direct bandgap has been estimated to be 0.9 eV via the hybrid functional method, which is smaller than the value of 1.6 eV of bulk material. The majority of vacancy defects and substitutional dopants change the electronic properties of the AlSb monolayer from semiconducting to metallic. Moreover, the Mg-Sb impurity has demonstrated the addition of ferromagnetic behavior to the material. It is revealed through the calculation of formation energy that in Al-rich conditions, the vacant site of V-Sb is the most stable, while in Sb-rich circumstances the point defect of V-Al gets the title. The formation energy has also been calculated for the substitutional dopants, showing relative stability of the defected structures. We undertook this theoretical study to inspire many experimentalists to focus their efforts on AlSb monolayer growth incorporating different impurities. It has been shown here that defect engineering is a powerful tool to tune the properties of novel AlSb two-dimensional monolayer for advanced nanoelectronic applications.
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| 21. |
- Balaz, Pavel, et al.
(författare)
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Transport theory for femtosecond laser-induced spin-transfer torques
- 2018
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 30:11
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser pulse is accompanied by a nonthermal spin-polarized current of hot electrons. These spin currents are studied here theoretically in a spin valve with noncollinear magnetizations. To this end, we introduce an extended model of superdiffusive spin transport that enables the treatment of noncollinear magnetic configurations, and apply it to the perpendicular spin valve geometry. We show how spin-transfer torques arise due to this mechanism and calculate their action on the magnetization present, as well as how the latter depends on the thicknesses of the layers and other transport parameters. We demonstrate that there exists a certain optimum thickness of the out-of-plane magnetized spin-current polarizer such that the torque acting on the second magnetic layer is maximal. Moreover, we study the magnetization dynamics excited by the superdiffusive spin-transfer torque due to the flow of hot electrons employing the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser pulse applied to one magnetic layer can excite small-angle precessions of the magnetization in the second magnetic layer. We compare our calculations with recent experimental results.
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| 22. |
- Banerjee, Saikat, et al.
(författare)
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Interacting Dirac materials
- 2020
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 32:40
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the extent to which the class of Dirac materials in two-dimensions provides general statements about the behavior of both fermionic and bosonic Dirac quasiparticles in the interacting regime. For both quasiparticle types, we find common features for the interaction induced renormalization of the conical Dirac spectrum. We perform the perturbative renormalization analysis and compute the self-energy for both quasiparticle types with different interactions and collate previous results from the literature whenever necessary. Guided by the systematic presentation of our results in table1, we conclude that long-range interactions generically lead to an increase of the slope of the single-particle Dirac cone, whereas short-range interactions lead to a decrease. The quasiparticle statistics does not qualitatively impact the self-energy correction for long-range repulsion but does affect the behavior of short-range coupled systems, giving rise to different thermal power-law contributions. The possibility of a universal description of the Dirac materials based on these features is also mentioned.
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| 23. |
- Bera, Sandip, et al.
(författare)
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Floquet scattering of quadratic band-touching semimetals through a time-periodic potential well
- 2021
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 33:29
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Tidskriftsartikel (refereegranskat)abstract
- We consider tunneling of quasiparticles through a rectangular quantum well, subject to periodic driving. The quasiparticles are the itinerant charges in two-dimensional and three-dimensional semimetals having a quadratic bandtouching (QBT) point in the Brillouin zone. To analyze the time-periodic Hamiltonian, we assume a non-adiabatic limit where the Floquet theorem is applicable. By deriving the Floquet scattering matrices, we chalk out the transmission and shot noise spectra of the QBT semimetals. The spectra show Fano resonances, which we identify with the (quasi)bound states of the systems.
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| 24. |
- Berggren, Karl-Fredrik, et al.
(författare)
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Basic modelling of transport in 2D wave-mechanical nanodots and billiards with balanced gain and loss mediated by complex potentials
- 2018
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 30:20
-
Tidskriftsartikel (refereegranskat)abstract
- Non-Hermitian quantum mechanics with parity-time (PT) symmetry is presently gaining great interest, especially within the fields of photonics and optics. Here, we give a brief overview of low-dimensional semiconductor nanodevices using the example of a quantum dot with input and output leads, which are mimicked by imaginary potentials for gain and loss, and how wave functions, particle flow, coalescence of levels and associated breaking of PT symmetry may be analysed within such a framework. Special attention is given to the presence of exceptional points and symmetry breaking. Related features for musical string instruments and wolf-notes are outlined briefly with suggestions for further experiments.
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| 25. |
- Bondarenko, Nina G., et al.
(författare)
-
Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain
- 2019
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 31:41
-
Tidskriftsartikel (refereegranskat)abstract
- Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrodinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that dnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.
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| 26. |
- Bonetti, Stefano
(författare)
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X-ray imaging of spin currents and magnetisation dynamics at the nanoscale
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:13
-
Forskningsöversikt (refereegranskat)abstract
- Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in x-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning x-ray transmission microscopy (STXM) at resonant soft x-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the x-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the x-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated x-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.
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| 27. |
- Bosio, Noemi, 1993, et al.
(författare)
-
Can oxygen vacancies in ceria surfaces be measured by O1s photoemission spectroscopy?
- 2022
-
Ingår i: Journal of physics. Condensed matter : an Institute of Physics journal. - 1361-648X .- 0953-8984. ; 34:17
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray photoemission spectroscopy is a standard technique for materials characterization and the O 1s binding energy is commonly measured for oxides. Here we use density functional theory calculations to investigate how the O 1s binding energy in CeO2(111) is influenced by the presence of oxygen vacancies. The case with point vacancies in CeO2(111) is compared to complete reduction to Ce2O3. Reduction of CeO2by oxygen vacancies is found to have a minor effect on the O 1s binding energy. The O 1s binding energy is instead clearly changed when the character of the chemical bond for the considered oxygen atom is modified by, for example, the formation of OH-groups or carbonates.
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| 28. |
- Botella, Pablo, PhD Student, et al.
(författare)
-
High-pressure characterization of multifunctional CrVO4
- 2020
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 32:38
-
Tidskriftsartikel (refereegranskat)abstract
- The structural stability and physical properties of CrVO4 under compression were studied by X-ray diffraction, Raman spectroscopy, optical absorption, resistivity measurements, and ab initio calculations up to 10 GPa. High-pressure X-ray diffraction and Raman measurements show that CrVO4 undergoes a phase transition from the ambient pressure orthorhombic CrVO4-type structure (Cmcm space group, phase III) to the high-pressure monoclinic CrVO4-V phase, which is isomorphic to the wolframite structure. Such a phase transition (CrVO4-type → wolframite), driven by pressure, also was previously observed in indium vanadate. The crystal structure of both phases and the pressure dependence in unit-cell parameters, Raman-active modes, resistivity, and electronic band gap, is reported. Vanadium atoms are sixth-fold coordinated in the wolframite phase, which is related to the collapse in the volume at the phase transition. Besides, we also observed drastic changes in the phonon spectrum, a drop of the band-gap, and a sharp decrease of resistivity. All the observed phenomena are explained with the help of first-principles calculations.
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| 29. |
- Bruckner, Barbara, et al.
(författare)
-
Electronic excitation of transition metal nitrides by light ions with keV energies
- 2020
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 32:40
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the specific electronic energy deposition by protons and He ions with keV energies in different transition metal nitrides of technological interest. Data were obtained from two different time-of-flight ion scattering setups and show excellent agreement. For protons interacting with light nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom were found, which coincide with literature data of N(2)gas for primary energies <= 25 keV. In case of the chemically rather similar nitrides with metal constituents from the 5(th)and 6(th)period, i.e. ZrN and HfN, the electronic stopping cross sections were measured to exceed what has been observed for molecular N(2)gas. For He ions, electronic energy loss in all nitrides was found to be significantly higher compared to the equivalent data of N(2)gas. Additionally, deviations from velocity proportionality of the observed specific electronic energy loss are observed. A comparison with predictions from density functional theory for protons and He ions yields a high apparent efficiency of electronic excitations of the target for the latter projectile. These findings are considered to indicate the contributions of additional mechanisms besides electron hole pair excitations, such as electron capture and loss processes of the projectile or promotion of target electrons in atomic collisions.
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| 30. |
- Carlström, Johan
(författare)
-
Spin-charge transformation of lattice fermion models : duality approach for diagrammatic simulation of strongly correlated systems
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:38
-
Tidskriftsartikel (refereegranskat)abstract
- I derive a dual description of lattice fermions, specifically focusing on the t-J and Hubbard models, that allow diagrammatic techniques to be employed efficiently in the strongly correlated regime, as well as for systems with a restricted Hilbert space. These constructions are based on spin-charge transformation, where the lattice fermions of the original model are mapped onto spins and spin-less fermions. This mapping can then be combined with Popov-Fedotov fermionisation, where the spins are mapped onto lattice fermions with imaginary chemical potential. The resulting models do not contain any large expansion parameters, even for strongly correlated systems. Also, they exhibit dramatically smaller corrections to the density matrix from nonlinear terms in the Hamiltonian. The combination of these two properties means that they can be addressed with diagrammatic methods, including simulation techniques based on stochastic sampling of diagrammatic expansions.
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| 31. |
- Carravetta, V, et al.
(författare)
-
X-ray absorption of molecular cations-a new challenge for electronic structure theory
- 2022
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 34:36, s. 363002-
-
Forskningsöversikt (refereegranskat)abstract
- In this paper we put forward some historical notes on the development of computational chemistry toward applications of x-ray spectroscopies. We highlight some of the important contributions by Enrico Clementi as method and program developer and as a supporter of this branch of computational research. We bring up a modern example based on the very recent experimental development of x-ray absorption of cationic molecules. As we show this spectroscopy poses new challenges for electronic structure theory and the electron correlation problem.
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| 32. |
- Cayao, Jorge
(författare)
-
Exceptional degeneracies in non-Hermitian Rashba semiconductors
- 2023
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 35:25
-
Tidskriftsartikel (refereegranskat)abstract
- Exceptional points (EPs) are spectral degeneracies of non-Hermitian (NH) systems where eigenvalues and eigenvectors coalesce, inducing unique topological phases that have no counterpart in the Hermitian realm. Here we consider an NH system by coupling a two-dimensional semiconductor with Rashba spin-orbit coupling (SOC) to a ferromagnet lead and show the emergence of highly tunable EPs along rings in momentum space. Interestingly, these exceptional degeneracies are the endpoints of lines formed by the eigenvalue coalescence at finite real energy, resembling the bulk Fermi arcs commonly defined at zero real energy. We then show that an in-plane Zeeman field provides a way to control these exceptional degeneracies although higher values of non-Hermiticity are required in contrast to the zero Zeeman field regime. Furthermore, we find that the spin projections also coalescence at the exceptional degeneracies and can acquire larger values than in the Hermitian regime. Finally, we demonstrate that the exceptional degeneracies induce large spectral weights, which can be used as a signature for their detection. Our results thus reveal the potential of systems with Rashba SOC for realizing NH bulk phenomena.
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| 33. |
- Chakraborty, Sudip, et al.
(författare)
-
Current computational trends in polyanionic cathode materials for Li and Na batteries
- 2018
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 30:28
-
Forskningsöversikt (refereegranskat)abstract
- A long-standing effort has been devoted for the development of high energy density cathodes both for Li-and Na-ion batteries (LIBs and SIBs). The scientific communities in battery research primarily divide the Li- and Na-ion cathode materials into two categories: layered oxides and polyanionic compounds. Researchers are trying to improve the energy density of such materials through materials screening by mixing the transition metals or changing the concentration of Li or Na in the polyanionic compounds. Due to the fact that there is more stability in the polyanionic frameworks, batteries based on these materials mostly provide a prolonged cycling life as compared to the layered oxide materials. Nevertheless, the bottleneck for such compounds is the weight penalty from polyanionic groups that results into the lower capacity. The anion engineering could be considered as an essential way out to design such polyanionic compounds to resolve this issue and to fetch improved cathode performance. In this topical review we present a systematic overview of the polyanionic cathode materials used for LIBs and SIBs. We will also present the computational methodologies that have become significantly relevant for battery research. We will make an attempt to provide the theoretical insight with a current development in sulfate (SO4), silicate (SiO4) and phosphate (PO4) based cathode materials for LIBs and SIBs. We will end this topical review with the future outlook, that will consist of the next generation organic electrode materials, mainly based on conjugated carbonyl compounds.
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| 34. |
- Chakravorty, Manotosh, et al.
(författare)
-
Proposed Bose-Einstein condensation of magnons in nanostructured films of Gd at low temperature and its manifestations in electrical resistivity and magnetoresistance
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:25
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the observation of a proposed Bose-Einstein condensation (BEC) of magnons in a temperature range of around 15-20 K in nanostructured films of Gd with grain sizes that are much larger than the size range where superparamagentism is expected. The observation was carried out using magnetic as well as high precision resistivity and magnetoresistance (MR) measurements performed to low temperatures. We observe that the experimental observations depend crucially on one parameter, namely softening of the spin wave stiffness parameter D at BEC and the resistivity as well as MR can be related quantitatively to magnetic measurements through the temperature variation of the constant D in the vicinity of the transition. This paper establishes that the BEC reported before in nanocrystalline Gd can be extended to a somewhat larger size range.
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| 35. |
- Chowdhury, Mouli Roy, et al.
(författare)
-
Antiferromagnetic short-range order and cluster spin-glass state in diluted spinel ZnTiCoO4
- 2022
-
Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:27
-
Tidskriftsartikel (refereegranskat)abstract
- The nature of magnetism in the doubly-diluted spinel ZnTiCoO4 = (Zn2+)( A ) [Ti4+Co2+]( B )O-4 is reported here employing the temperature and magnetic field (H) dependence of dc susceptibility (chi), ac susceptibilities (chi ' and chi ''), and heat capacity (C (p)) measurements. Whereas antiferromagnetic (AFM) Neel temperature T (N) = 13.9 K is determined from the peak in the partial differential (chi T)/ partial differential T vs T plot, the fit of the relaxation time tau (determined from the peak in the chi '' vs T data at different frequencies) to the Power law: tau = tau (0) [(T - T (SG))/T (SG)](-z nu ) yields the spin glass freezing temperature T (SG) = 12.9 K, z nu similar to 11.75, and tau (0) similar to 10(-12) s. Since the magnitudes of tau (0) and z nu depend on the magnitude of T (SG), a procedure is developed to find the optimum value of T (SG) = 12.9 K. A similar procedure is used to determine the optimum T (0) = 10.9 K in the Vogel-Fulcher law: tau = tau (0) exp[E (a)/k (B)(T - T (0))] yielding E (a)/k (B) = 95 K, and tau (0) = 1.6 x 10(-13) s. It is argued that the comparatively large magnitude of the Mydosh parameter omega = 0.026 and k (B) T (0)/E (a) = 0.115 (MUCH LESS-THAN1) suggests cluster spin-glass state in ZnTiCoO4 below T-SG. In the C (p) vs T data from 1.9 K to 50 K, only a broad peak near 20 K is observed. This and absence of lambda-type anomaly near T (N) or T (SG) combined with the reduced value of change in magnetic entropy from 50 K to 1.9 K suggests only short-range AFM ordering in the system, consistent with spin-glass state. The field dependence of T (SG) shows slight departure (phi similar to 4.0) from the non-mean-field Almeida-Thouless line T (SG)(H) = T (SG)(0) (1 - AH (2/phi )). Strong temperature dependence of magnetic viscosity S and coercivity H (C) without exchange bias, both tending to zero on approach to T (SG) from below, further support the spin-glass state which results from magnetic dilution driven by diamagnetic Zn2+ and Ti4+ ions leading to magnetic frustration. Magnetic phase diagram in the H-T plane is established using the high-field magnetization data M(H, T) for T < T (N) which reveals rapid decrease of T (SG) with increase in H whereas decrease in T (N) with increase in H is weaker, typical of AFM systems. For T > T (N), the data of chi vs T are fit to the modified Curie-Weiss law, chi = chi (0) + C/(T + theta), with chi (0) = 3.2 x 10(-4) emu mol(-1) Oe(-1) yielding theta = 4 K and C = 2.70 emu K mol(-1) Oe(-1). This magnitude of C yields effective magnetic moment = 4.65 mu (B) for Co2+, characteristic of Co2+ ions with some contribution from spin-orbit coupling. Molecular field theory with effective spin S = 3/2 of Co2+ is used to determine the nearest-neighbor exchange constant J (1)/k (B) = 2. 39 K AFM and next-nearest-neighbor exchange constant J (2)/k (B) = -0.66 K (ferromagnetic).
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| 36. |
- Chung, Suk Bum, et al.
(författare)
-
Special Issue on Solitons in Quantum Physics
- 2024
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 36:43
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This is an Editorial for the Special Issue on Solitons in Quantum Physics.
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| 37. |
- Dai, Jin, et al.
(författare)
-
Autonomous topological time crystals and knotty molecular motors
- 2021
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 33:1
-
Tidskriftsartikel (refereegranskat)abstract
- We show that topology is a very effective tool, to construct classical Hamiltonian time crystals. For this we numerically analyze a general class of time crystalline Hamiltonians that are designed to model the dynamics of molecular closed strings. We demonstrate how the time crystalline qualities of a closed string are greatly enhanced when the string becomes knotted. The Hamiltonians that we investigate include a generalized Kratky-Porod wormlike chain model in combination with long range Coulomb and Lennard-Jones interactions. Such energy functions are commonplace in coarse grained molecular modeling. Thus we expect that physical realizations of Hamiltonian time crystals can be constructed in terms of knotted ring molecules.
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| 38. |
- Das, Souvik, et al.
(författare)
-
Fano resonances in tilted Weyl semimetals in an oscillating quantum well
- 2024
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 36:39
-
Tidskriftsartikel (refereegranskat)abstract
- Considering the low-energy model of tilted Weyl semimetal, we study the electronic transmission through a periodically driven quantum well, oriented in the transverse direction with respect to the tilt. We adopt the formalism of Floquet scattering theory and investigate the emergence of Fano resonances as an outcome of matching between the Floquet sidebands and quasi-bound states. The Fano resonance energy changes linearly with the tilt strength suggesting the fact that tilt-mediated part of quasi-bound states energies depends on the above factor. Given a value of momentum parallel (perpendicular) to the tilt, we find that the energy gap between two Fano resonances, appearing for two adjacent values of transverse (collinear) momentum with respect to the tilt direction, is insensitive (sensitive) to the change in the tilt strength. Such a coupled (decoupled) behavior of tilt strength and the collinear (transverse) momentum can be understood from the tilt-mediated and normal parts of the quasi-bound state energies inside the potential well. We vary the other tilt parameters and chirality of the Weyl points to conclusively verify the exact form of the tilt-mediated part of the quasi-bound state energy that is the same as the tilt term in the static dispersion. The tilt orientation can significantly alter the transport in terms of evolution of Fano resoance energy with tilt momentum. We analytically find the explicit form of the bound state energy that further supports all our numerical findings. Our work paves the way to probe the tilt-mediated part of quasi-bound state energy to understand the complex interplay between the tilt and Fano resonance.
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| 39. |
- Davidsson, Joel, 1989-
(författare)
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Theoretical polarization of zero phonon lines in point defects
- 2020
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing. - 0953-8984 .- 1361-648X. ; 32:38
-
Tidskriftsartikel (refereegranskat)abstract
- In quantum technologies, point defects in semiconductors are becoming more significant. Understanding the frequency, intensity, and polarization of the zero phonon line is important. The last two properties are the subject of this paper. I present a method for calculating these properties and show the importance of using wave functions from both the ground and excited state. The validity of this method is demonstrated on the divacancy in 4H-SiC. Here, the calculated polarization and radiative lifetimes are in excellent agreement with experimental measurements. In general, this method can help to identify point defects and estimate suitable applications.
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| 40. |
- dos Santos Soares, Ricardo de Oliveira, et al.
(författare)
-
Membrane vesiculation induced by proteins of the dengue virus envelope studied by molecular dynamics simulations
- 2017
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:50
-
Tidskriftsartikel (refereegranskat)abstract
- Biological membranes are continuously remodeled in the cell by specific membrane-shaping machineries to form, for example, tubes and vesicles. We examine fundamental mechanisms involved in the vesiculation processes induced by a cluster of envelope (E) and membrane (M) proteins of the dengue virus (DENV) using molecular dynamics simulations and a coarse-grained model. We show that an arrangement of three E-M heterotetramers (EM3) works as a bending unit and an ordered cluster of five such units generates a closed vesicle, reminiscent of the virus budding process. In silico mutagenesis of two charged residues of the anchor helices of the envelope proteins of DENV shows that Arg-471 and Arg-60 are fundamental to produce bending stress on the membrane. The fine-tuning between the size of the EM3 unit and its specific bending action suggests this protein unit is an important factor in determining the viral particle size.
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| 41. |
- Ekholm, Marcus, et al.
(författare)
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The role of magnetic order in VOCl
- 2019
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 31:32
-
Tidskriftsartikel (refereegranskat)abstract
- VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V-V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.
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| 42. |
- Ektarawong, Annop, et al.
(författare)
-
Phase stability of three-dimensional bulk and two-dimensional monolayer As1-xSbx solid solutions from first principles
- 2019
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 31:24
-
Tidskriftsartikel (refereegranskat)abstract
- The mixing thermodynamics of both three-dimensional bulk and two-dimensional monolayered alloys of As1-xSbx as a function of alloy composition and temperature are explored using a first-principles cluster-expansion method, combined with canonical Monte-Carlo simulations. We observe that, for the bulk phase, As1-xSbx alloy can exhibit not only chemical ordering of As and Sb atoms at x = 0.5 to form an ordered compound of AsSb stable upon annealing up to T approximate to 475 K, but also a miscibility gap at 475 K less than or similar to T less than or similar to 550 K in which two disordered solid solutions of As1-xSbx of different alloy compositions thermodynamically coexist. At T amp;gt; 550 K, a single-phase solid solution of bulk As1-xSbx is predicted to be stable across the entire composition range. These results clearly explain the existing uncertainties in the alloying behavior of bulk As1-xSbx alloy, as previously reported in the literature, and also found to be in qualitative and quantitative agreement with the experimental observations. Interestingly, the alloying behavior of As1-xSbx is considerably altered, as the dimensionality of the material reduces from the three-dimensional bulk state to the two-dimensional monolayered state-for example, a single-phase solid solution of monolayer As1-xSbx is predicted to be stable over the whole composition range at T amp;gt; 250 K. This distinctly highlights an influence of the reduced dimensionality on the alloying behavior of As1-xSbx.
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| 43. |
- Ektarawong, Annop, 1987-, et al.
(författare)
-
Stability of SnSe1-xSx solid solutions revealed by first-principles cluster expansion
- 2018
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 30:29
-
Tidskriftsartikel (refereegranskat)abstract
- The configurational thermodynamics of a pseudo-binary alloy SnSe1-xSx in the Pnma phase is studied using first-principles cluster-expansion method in combination with canonical Monte Carlo simulations. We find that, despite the alloy having a tendency toward a phase decomposition into SnSe and SnS at 0 K, the two constituent binaries readily mix with each other to form random SnSe1-xSx solid solutions even at a temperature below room temperature. The obtained isostructural phase diagram of SnSe1-xSx reveals that the alloy is thermodynamically stable as a single-phase random solid solution over a whole composition range above 200 K. These findings provide a fundamental understanding on the alloying behavior of SnSe1-xSx and bring clarity to the debated clustering tendency in this alloy system.
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| 44. |
- Espinosa-Garcia, W. F., et al.
(författare)
-
The electronic and optical properties of the sulvanite compounds : a many-body perturbation and time-dependent density functional theory study
- 2018
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 30:3
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied, by means of first-principles calculations, the electronic and optical properties of the sulvanite family: Cu3MX4 (M = V, Nb, Ta and X = S, Se), which, due to its broad range of gaps and chemical stability, have emerged as promising materials for technological applications such as photovoltaics and transparent conductivity. To address the reliability of those properties we have used semi-local and hybrid functionals (PBEsol, HSE06), many-body perturbation theory (G(0)W(0) approximation and Bethe-Salpeter equation), and time-dependent density functional theory (revised bootstrap kernel) to calculate the quasi-particle dispersion relation, band gaps, the imaginary part of the macroscopic dielectric function and the absorption coefficient. The calculated valence band maximum and the conduction band minimum are located at the R and X-points, respectively. The calculated gaps using PBEsol are between 0.81 and 1.88 eV, with HSE06 into 1.73 and 2.94 eV, whereas the G(0)W(0) values fall into the 1.91-3.19 eV range. The calculated dielectric functions and absorption coefficients show that all these compounds present continuous excitonic features when the Bethe-Salpeter equation is used. Contrarily, the revised bootstrap kernel is incapable of describing the excitonic spectra. The calculated optical spectra show that Cu3VS4 and Cu3MSe4 have good absorption in the visible, whereas Cu3NbS4 and Cu3TaS4 have it on the near ultraviolet.
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| 45. |
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| 46. |
- Gaikwad, Prashant V., et al.
(författare)
-
Cluster assembly route to a novel octagonal two-dimensional ZnO monolayer
- 2017
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 29:33
-
Tidskriftsartikel (refereegranskat)abstract
- To explore the possibility of cluster assembly resulting in a two-dimensional (2D) stable monolayer of ZnO, a systematic study is performed on the structural evolution of bare and passivated stoichiometric clusters of ZnnOn, n = 1-8, using density-functional-theory-based first principles electronic structure calculations. The changes in hybridization are investigated with the aid of the site-projected partial density of states and partial charge density, while the effect of passivation and size on the ionicity of the cluster is studied using Bader charge analysis. The structural and chemical properties are found to be influenced by the coordination number of atoms in the clusters irrespective of the coordinating species. The physical parameters and hybridization of the states for the clusters on passivation resemble those of the bulk. Passivation thus provides an environment that leads to the stability of the clusters. Cluster assembly using the stable cluster geometries of passivated clusters (without the passivating atoms) has been shown to lead to stable 2D structures. This stability has been studied on the basis of binding energy, vibrational frequency, phonon dispersion and thermal properties. A new octagonal 2D monolayer planar geometry of ZnO is predicted.
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| 47. |
- Gerasimov, Arsenii, et al.
(författare)
-
Nature of the magnetic moment of cobalt in ordered FeCo alloy
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:16
-
Tidskriftsartikel (refereegranskat)abstract
- The magnets are typically classified into Stoner and Heisenberg type, depending on the itinerant or localized nature of the constituent magnetic moments. In this work, we investigate theoretically the behaviour of the magnetic moments of iron and cobalt in their B2-ordered alloy. The results based on local spin density approximation for the density functional theory (DFT) suggest that the Co magnetic moment strongly depends on the directions of the surrounding magnetic moments, which usually indicates the Stoner-type mechanism of magnetism. This is consistent with the disordered local moment picture of the paramagnetic state, where the magnetic moment of cobalt gets substantially suppressed. We argue that this is due to the lack of strong on-site electron correlations, which we take into account by employing a combination of DFT and dynamical mean-field theory (DMFT). Within LDA + DMFT, we find a substantial quasiparticle mass renormalization and a non Fermi-liquid behaviour of Fe-3d orbitals. The resulting spectral functions are in very good agreement with measured spin-resolved photoemission spectra. Our results suggest that local correlations play an essential role in stabilizing a robust local moment on Co in the absence of magnetic order at high temperatures.
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| 48. |
- Ghorai, Sagar, et al.
(författare)
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Evolution of Griffiths phase and critical behaviour of La1-xPbxMnO3 +/- y solid solutions
- 2021
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:14
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline La1-xPbxMnO3 +/- y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of x-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic (FM) phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (beta, gamma and delta) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of FM clusters. Long-range FM order is established as the result of long-range interactions between FM clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J kg(-1) at 5 T field) and a magnetic phase transition near room temperature.
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| 49. |
- Ghosh, Arnob Kumar, et al.
(författare)
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Generation of higher-order topological insulators using periodic driving
- 2024
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 36:9
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Forskningsöversikt (refereegranskat)abstract
- Topological insulators (TIs) are a new class of materials that resemble ordinary band insulators in terms of a bulk band gap but exhibit protected metallic states on their boundaries. In this modern direction, higher-order TIs (HOTIs) are a new class of TIs in dimensions d > 1. These HOTIs possess -dimensional boundaries that, unlike those of conventional TIs, do not conduct via gapless states but are themselves TIs. Precisely, an nth order d-dimensional higher-order TI is characterized by the presence of boundary modes that reside on its -dimensional boundary. For instance, a three-dimensional second (third) order TI hosts gapless (localized) modes on the hinges (corners), characterized by . Similarly, a second-order TI (SOTI) in two dimensions only has localized corner states (). These higher-order phases are protected by various crystalline as well as discrete symmetries. The non-equilibrium tunability of the topological phase has been a major academic challenge where periodic Floquet drive provides us golden opportunity to overcome that barrier. Here, we discuss different periodic driving protocols to generate Floquet HOTIs while starting from a non-topological or first-order topological phase. Furthermore, we emphasize that one can generate the dynamical anomalous π-modes along with the concomitant 0-modes. The former can be realized only in a dynamical setup. We exemplify the Floquet higher-order topological modes in two and three dimensions in a systematic way. Especially, in two dimensions, we demonstrate a Floquet SOTI (FSOTI) hosting 0- and π corner modes. Whereas a three-dimensional FSOTI and Floquet third-order TI manifest one- and zero-dimensional hinge and corner modes, respectively.
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| 50. |
- Ghosh, Sayandeep, et al.
(författare)
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Antiferromagnetism, spin-glass state, H-T phase diagram, and inverse magnetocaloric effect in Co2RuO4
- 2020
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 32:48
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Tidskriftsartikel (refereegranskat)abstract
- Static and dynamic magnetic properties of normal spinel Co2RuO4= (Co2+)A[Co3+Ru3+](B)O-4 are reported based on our investigations of the temperature (T), magnetic field (H) and frequency (f) dependence of the ac-magnetic susceptibilities and dc-magnetization (M) covering the temperature rangeT= 2 K-400 K and H up to 90 kOe. These investigations show that Co2RuO4 exhibits an antiferromagnetic (AFM) transition at T-N similar to 15.2 K, along with a spin-glass state at slightly lower temperature (T-SG) near 14.2 K. It is argued thatT(N)is mainly governed by the ordering of the spins of Co2+ ions occupying theA-site, whereas the exchange interaction between the Co2+ ions on theA-site and randomly distributed Ru(3+)on theB-site triggers the spin-glass phase, Co3+ ions on theB-site being in the low-spin non-magnetic state. Analysis of measurements ofM(H,T) for TT-N, analysis of the paramagnetic susceptibility (chi) vs.Tdata are fit to the modified Curie-Weiss law,chi=chi(0)+C/(T+theta), with chi(0)= 0.0015 emu mol(-1)Oe(-1)yielding theta= 53 K andC= 2.16 emu-K mol(-1)Oe(-1), the later yielding an effective magnetic moment mu(eff)= 4.16 mu(B)comparable to the expected value of mu(eff)= 4.24 mu(B)per Co2RuO4. Using T-N,theta and high temperature series for chi, dominant exchange constant J(1)/k(B)similar to 6 K between the Co(2+)on theA-sites is estimated. Analysis of the ac magnetic susceptibilities near T-SG yields the dynamical critical exponent z nu= 5.2 and microscopic spin relaxation time tau(0)similar to 1.16 x 10(-10)sec characteristic of cluster spin-glasses and the observed time-dependence ofM(t) is supportive of the spin-glass state. LargeM-Hloop asymmetry at low temperatures with giant exchange bias effect (H-EB similar to 1.8 kOe) and coercivity (H-C similar to 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed belowT(N)is interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) forT>T(N)to inverse MCE forT
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