| 1. |
- Adell, Johan, et al.
(författare)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 2469-9950 .- 2469-9969. ; 80:7
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Tidskriftsartikel (refereegranskat)abstract
- The initial growth of MnBi on MnAs-terminated (GaMn)As is studied by means of synchrotron-based photoelectron spectroscopy. From analysis of surface core-level shifts we conclude that a continued epitaxial MnBi layer is formed, in which the MnAs/MnBi interface occurs between As and Bi atomic planes. The well-defined 1×2 surface reconstruction of the MnAs surface is preserved for up to 2 ML of MnBi before clear surface degradation occurs. The MnBi layer appears to be free from intermixed As.
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| 2. |
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| 3. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of amorphous ices
- 2002
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 0163-1829 .- 1095-3795. ; 65:14
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivities κ of high-density amorphous (HDA) ice and low-density amorphous (LDA) ice were measured under pressure. The results for HDA show typical glasslike behavior, i.e., positive dκ/dT, whereas LDA exhibits crystal-like behavior, indicating that phonon-phonon scattering is dominant. LDA appears to be unique among apparently topologically disordered glasses to exhibit such behavior. Moreover, the results imply that LDA and glassy water formed by rapid cooling are different states.
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| 4. |
- Andreasson, Jakob, 1975, et al.
(författare)
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Electron-lattice interactions in the perovskite LaFe0.5Cr0.5O3 characterized by optical spectroscopy and LDA plus U calculations
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 80:7, s. 075103-
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Tidskriftsartikel (refereegranskat)abstract
- We use resonance Raman scattering (incident photon energies between 1.8 and 4.13 eV), LDA+U calculations, spectroscopic ellipsometry, and oblique IR reflectivity to characterize the strong electron-phonon interactions in the disordered perovskite LaFe0.5Cr0.5O3. When the photon energy coincides with a Cr to Fe Mott-Hubbard transfer gap around 2.4 eV the electron-phonon interaction is manifested by a Franck-Condon effect with exceptional first-and higher order scattering of a local oxygen breathing mode. At higher incident energies we observe a superposition of Franck-Condon scattering and Frohlich interaction induced infrared active longitudinal optical two-phonon scattering activated mainly by O to Fe charge transfer. Our results establish LaFe0.5Cr0.5O3 as a model compound for research on electron-phonon interactions in strongly correlated complex systems and show that Franck-Condon scattering in complex solids is not limited to Jahn-Teller active compounds.
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| 5. |
- Andreasson, Jakob, 1975, et al.
(författare)
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Electron-phonon interactions in perovskites containing Fe and Cr studied by Raman scattering using oxygen-isotope and cation substitution
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 78:23, s. 235103-
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Tidskriftsartikel (refereegranskat)abstract
- We use temperature-dependent inelastic light scattering to study the origin of the strong multiphonon scattering of a local oxygen breathing mode present in the mixed B-site orthorhombic (space group Pnma) perovskite LaFe0.5Cr0.5O3 but absent in isostructural LaFeO3 and LaCrO3. It is seen that the multiphonon scattering is critically sensitive to the presence of both Fe and Cr ions on the B site. These results support our interpretation that the multiphonon scattering is activated by local electron-phonon interactions according to the Franck-Condon picture following an Fe-Cr charge transfer. Further, O-18 substitution is performed on the x=0, 0.04, and 0.5 compounds and clearly shows that all modes appearing above the first-order phonon-scattering region in these compounds originate from higher-order oxygen stretching vibrations. In particular this is the case for the strong second-order scattering dominating the scattering response in LaFeO3. Accordingly we propose that these modes are generated by infrared-active longitudinal optical (IR LO) two-phonon and combination scattering activated by Frohlich interaction. For x=0.02 and 0.04 the characteristic IR LO two-phonon and Franck-Condon multiphonon-scattering profiles mix. We also study the influence of isovalent cation substitution and Sr doping in AFe(0.5)Cr(0.5)O(3) (A=La, Nd, and Gd) and La1-ySryFe0.5Cr0.5O3-delta (y=0, 0.16, and 0.5) on the strong electron-phonon coupling present in LaFe0.5Cr0.5O3. The Franck-Condon effect in LaFe0.5Cr0.5O3, is not significantly affected by isovalent A-site substitution, despite the increasing orthorhombic distortion associated with decreasing A-site ionic radii. On the contrary, aliovalent Sr doping causes a rapid decrease in the Franck-Condon scattering. This shows that the strong electron-phonon coupling in these compounds is highly sensitive to local lattice and electronic decoherence but insensitive to global lattice distortions. Finally, a preliminary assignment of the A(g) and B-2g phonon modes in AFe(0.5)Cr(0.5)O(3) (A=La, Nd, and Gd) is made based on the present observations and published results for LaCrO3 and AMnO(3). The modes associated with oxygen octahedral tilt and bending vibrations are heavily influenced by the magnitude of the orthorhombic distortion.
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| 6. |
- Berggren, Karl-Fredrik, 1937-, et al.
(författare)
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Effects of electron interactions at crossings of Zeeman-split subbands in quantum wires
- 2005
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 71:11, s. 115303-1-115303-5
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Tidskriftsartikel (refereegranskat)abstract
- Recent experimental studies of Zeeman-split one-dimensional subbands in ballistic quantum wires in an in-plane magnetic field show that additional nonquantized conductance structures occur as subbands cross at low electron densities [A. C. Graham et al., Phys. Rev.Lett. 91, 136404 (2003)]. These structures are called 0.7 analogs. We analyze the experimental transconductance data within the Kohn-Sham spin-density-functional method, including exchange and correlation effects for an infinite split-gate quantum wire in a parallel, in-plane magnetic field B∥. Energy levels are found to rearrange abruptly as they cross due to polarization effects driven by exchange and Coulomb interactions. Experimental qualitative features are explained well by this model. ©2005 The American Physical Society.
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| 7. |
- Berland, Kristian, 1983, et al.
(författare)
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Rings sliding on a honeycomb network: Adsorption contours, interactions, and assembly of benzene on Cu(111)
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 80:15, s. 155431-
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Tidskriftsartikel (refereegranskat)abstract
- Using a van der Waals density functional (vdW-DF) [Phys. Rev. Lett. 92, 246401 (2004)], we perform ab initio calculations for the adsorption energy of benzene (Bz) on Cu(111) as a function of lateral position and height. We find that the vdW-DF inclusion of nonlocal correlations (responsible for dispersive interactions) changes the relative stability of eight binding-position options and increases the binding energy by over an order of magnitude, achieving good agreement with experiment. The admolecules can move almost freely along a honeycomb web of “corridors” passing between fcc and hcp hollow sites via bridge sites. Our diffusion barriers (for dilute and two condensed adsorbate phases) are consistent with experimental observations. Further vdW-DF calculations suggest that the more compact (hexagonal) Bz-overlayer phase, with lattice constant a=6.74 Å, is due to direct Bz-Bz vdW attraction, which extends to ~8 Å. We attribute the second, sparser hexagonal Bz phase, with a=10.24 Å, to indirect electronic interactions mediated by the metallic surface state on Cu(111). To support this claim, we use a formal Harris-functional approach to evaluate nonperturbationally the asymptotic form of this indirect interaction. Thus, we can account well for benzene self-organization on Cu(111).
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| 8. |
- Bezugly, Eugene, et al.
(författare)
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Subgap current in superconducting tunnel junctions with diffusive electrodes
- 2006
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 73
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Tidskriftsartikel (refereegranskat)abstract
- We calculate subgap current in planar superconducting tunnel junctions with thin-film diffusive leads. It is found that the subharmonic gap structure of the tunnel current scales with an effective tunneling transparency which may exceed the junction transparency by up to two orders of magnitude depending on the junction geometry, and the ratio between the coherence length and the elastic scattering length. These results provide an alternative explanation of anomalously high values of the subgap current in tunnelling experiments often ascribed to imperfectness of the insulating layer. We also discuss the effect of finite lifetime of quasiparticles as the possible origin of additional enhancement of multiparticle tunnel currents.
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| 9. |
- Bezuglyi, Eugene, et al.
(författare)
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Nonequilibrium effects in tunnel Josephson junctions
- 2005
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 72
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Tidskriftsartikel (refereegranskat)abstract
- We study nonequilibrium effects in current transport through voltage biased tunnel junction with long diffusive superconducting leads at low applied voltage eV 2Δ, and finite temperatures. Due to a small value of the Josephson frequency, the quasiparticle spectrum adiabatically follows the time evolution of the superconducting phase difference, which results in the formation of oscillating bound states in the vicinity of the tunnel junction (Andreev band). The quasiparticles trapped by the Andreev band generate higher even harmonics of the. Josephson ac current, and also, in the presence of inelastic scattering, a nonequilibrium dc current, which may considerably exceed the dc quasiparticle current given by the tunnel model. The distribution of traveling quasiparticles also deviates from the equilibrium due to the spectrum oscillations, which results in an additional contribution to the dc current, proportional to V.
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| 10. |
- Boikov, Yu A., et al.
(författare)
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Effect of interfaces on the dielectric response of a SrTi O3 layer between metallic oxide electrodes
- 2006
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 74:2
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the dielectric permittivity ε of an 800 nm thick SrTi O3 layer in epitaxial SrRu O3 SrTi O3 SrRu O3 and Y Ba2 Cu3 O7-δ SrTi O3 SrRu O3 heterostructures followed the relation ε-1 = ε0 -1 C0 -1 (T- TCW) + εI -1, where C0 and TCW are the Curie constant and the Curie-Weiss temperature for the strontium titanate bulk crystal, respectively. The effective dielectric constant is lower than the bulk value due to the interfaces of the SrTi O3 film to its electrodes as given by εI. The εI was diminished roughly 2.5 times when the top SrRu O3 electrode in the trilayer was replaced by one of Y Ba2 Cu3 O7-δ. The capacitances Ci per unit area of the SrRu O3 SrTi O3 and Y Ba2 Cu3 O7-δ SrTi O3 interfaces were 8.2 and 2.3 F cm2, respectively. Characteristic penetration depths L of the electric field into the SrRu O3 and Y Ba2 Cu3 O7-δ electrodes were extracted from the Ci s and are several times larger than corresponding data estimated from free electron type models of metals. A diminished charge carrier density in the electrode very close to the interface is a likely reason for the enhanced L. © 2006 The American Physical Society.
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