| 1. |
- Abergel, David, et al.
(author)
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Infrared absorption of closely aligned heterostructures of monolayer and bilayer graphene with hexagonal boron nitride
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - : AMER PHYSICAL SOC. - 1098-0121 .- 1550-235X. ; 92:11
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Journal article (peer-reviewed)abstract
- We model optical absorption of monolayer and bilayer graphene on hexagonal boron nitride for the case of closely aligned crystal lattices. We show that perturbations with different spatial symmetry can lead to similar absorption spectra. We suggest that a study of the absorption spectra as a function of the doping for an almost completely full first miniband is necessary to extract meaningful information about the moire characteristics from optical absorption measurements and to distinguish between various theoretical proposals for the physically realistic interaction. Also, for bilayer graphene, the ability to compare spectra for the opposite signs of electric-field-induced interlayer asymmetry might provide additional information about the moire parameters.
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| 2. |
- Agterberg, Daniel F., et al.
(author)
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Checkerboard order in vortex cores from pair-density-wave superconductivity
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:10
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Journal article (peer-reviewed)abstract
- We consider competing pair-density-wave (PDW) and d-wave superconducting states in a magnetic field. We show that PDW order appears in the cores of d-wave vortices, driving checkerboard charge-density-wave (CDW) order in the vortex cores, which is consistent with experimental observations. Furthermore, we find an additional CDW order that appears on a ring outside the vortex cores. This CDW order varies with a period that is twice that of the checkerboard CDW and it only appears where both PDW and d-wave order coexist. The observation of this additional CDW order would provide strong evidence for PDW order in the pseudogap phase of the cuprates. We further argue that the CDW seen by nuclear magnetic resonance at high fields is due to a PDW state that emerges when a magnetic field is applied.
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| 3. |
- Aikebaier, Faluke, et al.
(author)
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Effects of short-range electron-electron interactions in doped graphene
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:15
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Journal article (peer-reviewed)abstract
- We study theoretically the effects of short-range electron-electron interactions on the electronic structure of graphene, in the presence of substitutional impurities. Our computational approach is based on the π orbital tight-binding model for graphene, with the electron-electron interactions treated self-consistently at the level of the mean-field Hubbard model. The finite impurity concentration is modeled using the supercell approach. We compare explicitly noninteracting and interacting cases with varying interaction strength and impurity potential strength. We focus in particular on the interaction-induced modifications in the local density of states around the impurity, which is a quantity that can be directly probed by scanning tunneling spectroscopy of doped graphene. We find that the resonant character of the impurity states near the Fermi level is enhanced by the interactions. Furthermore, the size of the energy gap, which opens up at high-symmetry points of the Brillouin zone of the supercell upon doping, is significantly affected by the interactions. The details of this effect depend subtly on the supercell geometry. We use a perturbative model to explain these features and find quantitative agreement with numerical results.
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| 4. |
- Alling, Björn, et al.
(author)
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Dynamic and structural stability of cubic vanadium nitride
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 91:5, s. 054101-
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Journal article (peer-reviewed)abstract
- Structural phase transitions in epitaxial stoichiometric VN/MgO(011) thin films are investigated using temperature-dependent synchrotron x-ray diffraction (XRD), selected-area electron diffraction (SAED), resistivity measurements, high-resolution cross-sectional transmission electron microscopy, and ab initio molecular dynamics (AIMD). At room temperature, VN has the B1 NaCl structure. However, below T-c = 250 K, XRD and SAED results reveal forbidden (00l) reflections of mixed parity associated with a noncentrosymmetric tetragonal structure. The intensities of the forbidden reflections increase with decreasing temperature following the scaling behavior I proportional to (T-c - T)(1/2). Resistivity measurements between 300 and 4 K consist of two linear regimes resulting from different electron/phonon coupling strengths in the cubic and tetragonal-VN phases. The VN transport Eliashberg spectral function alpha F-2(tr)(h omega), the product of the phonon density of states F(h omega) and the transport electron/phonon coupling strength alpha(2)(tr)(h omega), is determined and used in combination with AIMD renormalized phonon dispersion relations to show that anharmonic vibrations stabilize the NaCl structure at T greater than T-c. Free-energy contributions due to vibrational entropy, often neglected in theoretical modeling, are essential for understanding the room-temperature stability of NaCl-structure VN, and of strongly anharmonic systems in general.
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| 5. |
- Andersson, Andreas, et al.
(author)
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Modeling and simulations of quantum phase slips in ultrathin superconducting wires
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 91:13
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Journal article (peer-reviewed)abstract
- We study quantum phase slips (QPS) in ultrathin superconducting wires. Starting from an effective one-dimensional microscopic model, which includes electromagnetic fluctuations, we map the problem to a (1+1)-dimensional gas of interacting instantons. We introduce a method to calculate the tunneling amplitude of quantum phase slips directly from Monte Carlo simulations. This allows us to go beyond the dilute instanton gas approximation and study the problem without any limitations of the density of QPS. We find that the tunneling amplitude shows a characteristic scaling behavior near the superconductor-insulator transition. We also calculate the voltage-charge relation of the insulating state, which is the dual of the Josephson current-phase relation in ordinary superconducting weak links. This evolves from a sinusoidal form in the regime of dilute QPS to more exotic shapes for higher QPS densities, where interactions are important.
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| 6. |
- Aperis, Alex, et al.
(author)
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Multiband full-bandwidth anisotropic Eliashberg theory of interfacial electron-phonon coupling and high-Tc superconductivity in FeSe/SrTiO3
- 2018
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 97
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Journal article (peer-reviewed)abstract
- We examine the impact of interfacial phonons on the superconducting state of FeSe/SrTiO3 developing a material's specific multiband, full bandwidth, and anisotropic Eliashberg theory for this system. Our self-consistent calculations highlight the importance of the interfacial electron-phonon interaction, which is hidden behind the seemingly weak-coupling constant λm=0.4, in mediating the high Tc, and explain other puzzling experimental observations, such as the s-wave symmetry and replica bands. We discover that the formation of replica bands has a Tc decreasing effect that is nevertheless compensated by deep Fermi-sea Cooper pairing which has a Tc enhancing effect. We predict a strong-coupling dip-hump signature in the tunneling spectra due to the interfacial coupling.
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| 7. |
- Arapan, Sergiu, et al.
(author)
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Volume-dependent electron localization in ceria
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 91:12
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Journal article (peer-reviewed)abstract
- We have performed a numerical study of the process of electron localization in reduced ceria. Our results show that different localized charge distributions can be attained in a bulk system by varying the lattice parameter. We demonstrate that the effect of electron localization is mainly determined by lattice relaxation and an accurate account for the effects of electronic correlation is necessary to achieve localized charge distribution.
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| 8. |
- Azimi Mousolou, Vahid, et al.
(author)
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Spin-electric Berry phase shift in triangular molecular magnets
- 2016
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 94:23
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Journal article (peer-reviewed)abstract
- We propose a Berry phase effect on the chiral degrees of freedom of a triangular magnetic molecule. The phase is induced by adiabatically varying an external electric field in the plane of the molecule via a spin-electric coupling mechanism present in these frustrated magnetic molecules. The Berry phase effect depends on spin-orbit interaction splitting and on the electric dipole moment. By varying the amplitude of the applied electric field, the Berry phase difference between the two spin states can take any arbitrary value between zero and π, which can be measured as a phase shift between the two chiral states by using spin-echo techniques. Our result can be used to realize an electric-field-induced geometric phase-shift gate acting on a chiral qubit encoded in the ground-state manifold of the triangular magnetic molecule.
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| 9. |
- Bayat, A., et al.
(author)
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Universal single-frequency oscillations in a quantum impurity system after a local quench
- 2015
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In: Physical Review B. - 1098-0121. ; 92:15
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Journal article (peer-reviewed)abstract
- Universal single-frequency oscillations in the local nonequilibrium dynamics of a quantum many-body system are an exceptional phenomenon. In fact, till now, this has never been observed or predicted for the physically relevant case where a system is prepared to be quenched from one quantum phase to another. Here we show how the quench dynamics of the entanglement spectrum may reveal the emergence of such oscillations in a correlated quantum system with Kondo impurities. The oscillations we find are characterized by a single frequency. This frequency is independent of the amount of energy released by the local quench, and scales with the inverse system size. Importantly, the quench-independent frequency manifests itself also in local observables, such as the spin-spin correlation function of the impurities.
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| 10. |
- Baym, Gordon, et al.
(author)
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Transport in ultradilute solutions of He-3 in superfluid He-4
- 2015
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:2
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Journal article (peer-reviewed)abstract
- We calculate the effect of a heat current on transporting He-3 dissolved in superfluid He-4 at ultralow concentration, as will be utilized in a proposed experimental search for the electric dipole moment of the neutron (nEDM). In this experiment, a phonon wind will be generated to drive (partly depolarized) 3He down a long pipe. In the regime of 3He concentrations less than or similar to 10(-9) and temperatures similar to 0.5 K, the phonons comprising the heat current are kept in a flowing local equilibrium by small angle phonon-phonon scattering, while they transfer momentum to the walls via the He-4 first viscosity. On the other hand, the phonon wind drives the 3He out of local equilibrium via phonon-He-3 scattering. For temperatures below 0.5 K, both the phonon and He-3 mean free paths can reach the centimeter scale, and we calculate the effects on the transport coefficients. We derive the relevant transport coefficients, the phonon thermal conductivity, and the He-3 diffusion constants from the Boltzmann equation. We calculate the effect of scattering from the walls of the pipe and show that it may be characterized by the average distance from points inside the pipe to the walls. The temporal evolution of the spatial distribution of the He-3 atoms is determined by the time dependent He-3 diffusion equation, which describes the competition between advection by the phonon wind and He-3 diffusion. As a consequence of the thermal diffusivity being small compared with the He-3 diffusivity, the scale height of the final He-3 distribution is much smaller than that of the temperature gradient. We present exact solutions of the time dependent temperature and He-3 distributions in terms of a complete set of normal modes.
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