| 1. |
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| 2. |
- Durakiewicz, T., et al.
(författare)
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Observation of a kink in the dispersion of f-electrons
- 2008
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 84:3, s. 37003-
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Tidskriftsartikel (refereegranskat)abstract
- Strong interactions in correlated electron systems may result in the formation of heavy quasiparticles that exhibit kinks in their dispersion relation. Spectral weight is incoherently shifted away from the Fermi energy, but Luttinger's theorem requires the Fermi volume to remain constant. Our angle-resolved photoemission study of USb2 reveals a kink in a noncrossing 5f band, representing the first experimental observation of a kink structure in f-electron systems. The kink energy scale of 21 meV and the ultra-small peak width of 3 meV are observed. We propose the novel mechanism of renormalization of a point-like Fermi surface, and that Luttinger's theorem remains applicable.
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| 3. |
- Guziewicz, E., et al.
(författare)
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Mn on the surface of ZnO(0001) - a resonant photoemisson study
- 2005
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T115, s. 541-544
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of Mn/ZnO system has been invesigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage Mn-Theta <= 4 ML. Photoemission spectra taken near the Mn3p-Mn3d absorption edge after each deposition step show resonant enhancement of Mn3d states within 10 eV of the Fermi edge. The experimentally deduced partial Mn3d density of states for Theta >= 1.2 ML shows at least three features: a major Mn3d structure at 3.8-4.5 eV below the Fermi edge, a valence structure at lower binding energy (1-3 eV) and a broad satelite in the 5.5-9 eV range. The branching ratio of satellite/main structure increases with depostion from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 degrees C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surfaces as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4 eV, which shows that at least two manganese states are observed in the Mn-ZnO interface region.
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| 4. |
- Guziewicz, E., et al.
(författare)
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Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1046-1050
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Konferensbidrag (refereegranskat)abstract
- We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160 degrees C and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of foreign phases and metal accumulations as indicated by TEM data. The electronic structure of (Zn,Co)O films was studied by Resonant Photoemission Spectroscopy across the Co3p-Co3d photoionization threshold. We have observed that the resonant enhancement of the photoemission intensity from the Co3d shell is not the same for samples with different cobalt content. We suggest that the Co3d contribution to the valence band depends on both Co and H content. (C) 2011 Elsevier Ltd. All rights reserved.
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| 5. |
- Kowalik, Iwona, et al.
(författare)
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Structural and optical properties of low-temperature ZnO films grown by atomic layer deposition with diethylzinc and water precursors
- 2009
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 311:4, s. 1096-1101
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Tidskriftsartikel (refereegranskat)abstract
- We report on properties of low-temperature (LT) ZnO films grown by the atomic layer deposition method with diethylzinc (DEZn) precursor. It is shown that the ZnO thin film crystallographic orientation, quality of the surface, and optical properties depend on the main growth parameters like temperature, pulsing, and purging time and thus can be varied in controllable manner. All the presented results were obtained for ZnO layers grown at temperature between 90 and 200 degrees C. (C) 2008 Elsevier B.V. All rights reserved.
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| 6. |
- Godlewski, M, et al.
(författare)
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Influence of structural properties and of growth conditions on exciton properties in ZnCdSe/ZnSe quantum well structures
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 63-66
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Konferensbidrag (refereegranskat)abstract
- Structural and optical properties of relaxed and pseudomorphic ZnCdSe/ZnSe quantum well heterostructures are described. Structural quality and strain conditions of the films are linked with their light emission properties. From the temperature dependence of photoluminescence (PL) spectra we estimate exciton coupling constants to acoustic phonons in pseudomorphic and relaxed structures. The coupling is noticeably weaker in strain-relaxed structures with strong localization effects. PL kinetic studies confirm strong localization of excitons in strain-relaxed structures.
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| 7. |
- Guziewicz, E., et al.
(författare)
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Angle-resolved photoemission study of dispersive and narrow-band 5f states in UAsSe
- 2006
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 73:15, s. 155119-
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of ferromagnetic UAsSe have been investigated by angle-resolved photoemission spectroscopy (ARPES) in the photon energy range between 20 eV and 110 eV. Electron kinetic energy intensities are collected as a function of angle and mapped onto the materials reciprocal space. Energy-band mapping has been carried out both for a several-eV-wide energy interval as well as for a narrow energy interval of less than 1 eV from the Fermi energy. The main features of the deduced energy bands can be explained by band-structure calculations. In the interval close to the Fermi energy, the very high energy and momentum resolution allows the observation of a narrow, yet dispersive photoemission peak mainly of 5f character situated within 50 meV of the Fermi energy. The Lorentzian linewidth was found to be about 35 meV with a dispersion of 30 meV along the Gamma to Z direction and 40 meV dispersion along the Gamma to X direction in the Brillouin zone. We have also found broader (linewidth about 70 meV), hybridized f-character bands with a conventional dispersion of about 1 eV along the Gamma to X and the Z to R directions in the Brillouin zone. An intriguing electronic structure emerges for UAsSe in which both relatively dispersive and narrow 5f bands are present. The occurrence of 5f-band dispersions stipulates that the electronic structure of UAsSe requires lattice periodicity to be taken into account.
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| 8. |
- Joyce, J. J., et al.
(författare)
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Dual nature of the 5f electrons in plutonium materials
- 2006
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 378-80, s. 920-924
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of select Pu materials is examined by means of photoemission (PES) and model calculations. We present the first photoemission results and electronic structure calculations for the material PuIn3. Results for Pu materials, including the cubic delta-phase metal and the superconductor PuCoGa5, give indication of the 5f electrons exhibiting both localized and itinerant character. These new results for PuIn3 place this compounds also in the 5f dual nature category. The dual nature of the Pu 5f electrons demarks the boundary between localized and itinerant 5f character in the actinides. The photoemission data for delta-Pu, PuIn3 and PuCoGa5 are compared against model calculations. The calculations are a mixed level model (MLM) which is a multi-electron extension of the generalized gradient approximation. Using the MLM, one obtains good agreement for the volume and total energy minimum with 4 of 5 Pu 5f electrons localized. The calculations also agree well with the PES spectra. Other computational schemes and interpretations are also reviewed.
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| 9. |
- Joyce, J.J., et al.
(författare)
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Photoemission and the electronic structure of PuGaCo$_5$
- 2003
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Ingår i: Physical Review Letters. ; 91, s. 176401-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.
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| 10. |
- Kowalik, I. A., et al.
(författare)
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Soft x-ray absorption spectroscopy on Co doped ZnO : structural distortions and electronic structure
- 2016
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Ingår i: 16th International Conference On X-Ray Absorption Fine Structure (XAFS16). - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- We present soft x-ray absorption spectra from a series of Co doped ZnO films. We discuss systematic variations of the Co L-edge white line intensity and multiplet features for this series of samples. We document sizeable differences in the electronic state of the Co ionic cores, as well as in the local environment of the host lattice atoms, characterised by means of x-ray absorption spectra at the O K-edge and Zn L-edges. Model calculations allow to correlate the observed effects to small structural distortions of the ZnO lattice.
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| 11. |
- Polley, C. M., et al.
(författare)
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Observation of surface states on heavily indium-doped SnTe(111), a superconducting topological crystalline insulator
- 2016
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 93:7
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Tidskriftsartikel (refereegranskat)abstract
- The topological crystalline insulator tin telluride is known to host superconductivity when doped with indium (Sn1-xInxTe), and for low indium content (x=0.04) it is known that the topological surface states are preserved. Here we present the growth, characterization, and angle resolved photoemission spectroscopy analysis of samples with much heavier In doping (up to x≈0.4), a regime where the superconducting temperature is increased nearly fourfold. We demonstrate that despite strong p-type doping, Dirac-like surface states persist.
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| 12. |
- Sawicki, M., et al.
(författare)
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Homogeneous and heterogeneous magnetism in (Zn,Co)O : From a random antiferromagnet to a dipolar superferromagnet by changing the growth temperature
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:8
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Tidskriftsartikel (refereegranskat)abstract
- A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 degrees C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S = 3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x = 0.16 and 0.4. At higher growth temperature (200 degrees C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
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| 13. |
- Yang, X, et al.
(författare)
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Unusual quasiparticle renormalizations from angle resolved photoemission on USb2
- 2009
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Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 89:22-24, s. 1893-1911
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band, which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. Furthermore, the inferred quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band that does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy, involving transitions from the osculating band into a band that does cross the Fermi energy.
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