| 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. |
- 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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| 4. |
- 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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| 5. |
- Breitholtz, Marcus, 1974, et al.
(författare)
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Overlayer resonance and quantum well state of Cs/Cu(111) studied with angle-resolved photoemission, LEED, and first-principles calculations
- 2007
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Ingår i: Physical Review B. - 1098-0121. ; 75:15, s. 9-
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoemission spectroscopy and low-energy electron diffraction are used to study submonolayer coverages of Cs on Cu(111) at room temperature (RT) and 170 K. At RT, the Cs saturation coverage is approximately 90% of the full monolayer coverage. The full monolayer is characterized by a quantum well state (QWS) band having an energy of 25 meV below the Fermi level (E-F) in the (Gamma) over bar point and a resonance band extending to energies below the Cu band gap. This is supported by our first-principles calculations. Low-energy electron diffraction shows that the Cs overalyer forms a (2x2) structure over a wide coverage range, in which the QWS has energies from 50 meV above to 25 meV below E-F. The continued energy shift of the QWS after saturation of the diffraction angles is interpreted in terms of vacancies in the overlayer.
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| 6. |
- Dudiy, Sergey V., et al.
(författare)
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Wetting of TiC and TiN by metals
- 2004
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Ingår i: Physical Review B. - 1098-0121. ; 69:12
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Gorelik, Leonid, 1952, et al.
(författare)
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Giant shot noise due to mechanical transportation of spin-polarized electrons
- 2008
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Ingår i: Physical Review B. - 1098-0121. ; 77:17, s. 174304-
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Tidskriftsartikel (refereegranskat)abstract
- We show that single-electron "shuttling" of electrons in a magnetic nanoelectromechanical single-electron transistor device can be an efficient tool for studying electron spin-flip relaxation on quantum dots. The reason is traced to a spin blockade of the mechanically aided shuttle current that occurs in devices with highly polarized and collinearly magnetized leads. This results in giant peaks in the shot-noise spectral function, wherein the peak heights are only limited by the rate of electronic spin flips. Therefore, we show that nanomechanical spectroscopy of the spin-flip rate is possible, allowing spin-flip relaxation times as long as 10 mu s to be detected.
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| 8. |
- Granath, Mats, 1972, et al.
(författare)
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Anharmonic softening of Raman active phonons in iron-pnictides: Estimating the Fe isotope effect due to anharmonic expansion
- 2009
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Ingår i: Physical Review B. - 1098-0121. ; 79:23, s. 235103-
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Tidskriftsartikel (refereegranskat)abstract
- We present Raman measurements on the iron-pnictide superconductors CeFeAsO1-xFx and NdFeAsO1-xFx. Modeling the Fe-As plane in terms of harmonic and a cubic anharmonic Fe-As interactions, we calculate the temperature dependence of the energy and lifetime of the Raman active Fe B-1g mode and fit to the observed energy shift. The shifts and lifetimes are in good agreement with those measured also in other Raman studies which demonstrate that the phonon spectrum, at least at small wave numbers, is well represented by phonon-phonon interactions without any significant electronic contribution. Even at zero temperature there is a non-negligent effect of interactions on the phonon energy, which for the Fe B-1g mode corresponds to 6 cm(-1) or 3% of the total energy of the mode. We also estimate the anharmonic expansion from Fe (56 -> 54) isotope substitution to Delta a approximate to 5.1 x 10(-4) angstrom and Delta d(Fe-As) approximate to 2.5 x 10(-4) angstrom and the shift of harmonic zero-point fluctuations of bond lengths less than or similar to 3 x 10(-5) angstrom(2), giving a total relative average decrease in electronic hopping integrals of vertical bar delta vertical bar/t less than or similar to 2.0 x 10(-4). For a nonphonon-mediated weak-coupling superconductor this gives an isotope exponent alpha similar to 10(-2). The results pose a serious challenge for any theory of superconductivity in the pnictides that does not include electron-phonon interactions to produce a sizable Fe isotope effect.
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| 9. |
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| 10. |
- Holmlund, Joakim, 1968, et al.
(författare)
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Resonant two-phonon Raman scattering as a probe of hole crystal formation in Sr14?xCaxCu24O41
- 2006
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 74
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Tidskriftsartikel (refereegranskat)abstract
- The charge dynamics of the spin ladder compound Sr14-xCaxCu24O41 with x=0,6,13.6 has been investigated using wavelength- and temperature-dependent phonon Raman scattering on single crystals. In the unsubstituted, x=0, compound, a set of sharp two-phonon lines shows a strong increase in intensity below T similar to 200 K for light polarized along the ladder layer and with excitation energy close to the charge transfer gap similar to 1.9 eV. The temperature dependence of the strongly enhanced two-phonon bands below 200 K closely follows the recently reported formation of a standing charge density wave in the ladders [P. Abbamonte , Nature 431, 1078 (2004)]. Upon calcium substitution the polarized resonant Raman response rapidly decreases, signaling an increase of hole mobility in the ladder units. Temperature-dependent measurements of the x=13.6 sample indicate mobility of holes down to
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