Results 1 - 10 of 8174
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[en] Using the density functional theory and its combination to the dynamical mean field theory (DMFT), we have studied the electronic and magnetic structures of Fe-based superconductors, Fe2As2(A=Ca, Sr, Ba). Our results for the electronic structure agree well with existing angle resolved photoemission spectroscopy (ARPES) data. The temperature dependent magnetization has been calculated using DMFT, and the magnetic transition temperatures are reasonably consistent with the experimentally observed trend for three compounds.
[en] The electronic band structure of InSb(111) along the Γ-Λ-L<111> direction was determined using angle-resolved photoemission spectroscopy for the photon energy between 9 and 39 eV via synchrotron radiation. The bulk band dispersion is in agreement with earlier theoretical calculations. The In- (group III-) terminated InSb(111) surface shows surface Umklapp transitions and reflection of the bulk density of states. We found two nondispersive features which were not reported before. They are related to the surface state and the resonance process of the InSb(111)-2x2. (author)
[en] The electronic structure of the V(100) surface has been studied by means of angularly resolved photoelectron spectroscopy (ARUPS) and momentum- ( k-) resolved inverse photoemission spectroscopy (KRIPES). A narrow peak in the photoemission spectrum which is seen at the Fermi level is attributed to a transition from a surface resonance. The existence of this surface resonance at the Fermi level of the V(100) surface is potentially very important for the occurrence of the expected magnetic ordering of this surface. The energy of the critical point H25', which defines the top of the unoccupied part of the 3d band, has been determined to be within 3.0-3.2 eV above EF from the normal incidence KRIPES spectra. (author)
[en] We make a detailed study of the Eliashberg theory in the coupling region where some fundamental qualitative deviations from the conventional BCS- like behavior begin to appear. These deviations are identified as the onset of a cross-over from BCS superconductivity to Bose condensation. We point out that the beginning of this cross-over occurs when the gap Δg becomes comparable to the boson energies Ωph. This condition traduces the physical constraint that the distance the paired electron covers during the absorption of the virtual boson, cannot be larger than the coherence length. The frontier region of couplings is of the order of λ∼3, and high-Tc, materials are concerned. A clear qualitative indication of the occurrence of a cross-over regime should be a dip structure above the gap in the density of states of excitations, and this is one of the most robust characteristics of the high-Tc, superconducting state. Comparing our results with tunneling and photoemission experiments we conclude that high-Tc materials (cuprates and fullerides) are indeed at the beginning of a cross-over from BCS superconductivity to Bose condensation, even though the fermionic nature still prevails. If the Uemura plot is relevant, then the dip should also be present in the other materials that are close to the cross-over regime like heavy Fermion and organic superconductors. In all these materials Ginzburg Landau equations are irrelevant. (orig.)
[en] The resonating valence bond--Luttinger liquid theory for the high-Tc normal state permits some predictions about the effect of superconductivity on two measures of the one-particle Green's function: angle-resolved photoemission and tunneling for a high-Tc--insulator--high-Tc junction. These are compared to preliminary experimental data