Showing papers by "Ove Jepsen published in 2002"
TL;DR: In this paper, the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport in MgB2.
Abstract: A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB2 However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity No such correlation has been observed We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport
281 citations
TL;DR: In this paper, a theoretical model for quasiparticle and Josephson tunneling in multiband superconductors is developed and applied to MgB2-based junctions, and the gap functions in different bands in Mg-B2 are obtained from an extended Eliashberg formalism, using the results of band structure calculations.
Abstract: A theoretical model for quasiparticle and Josephson tunneling in multiband superconductors is developed and applied to MgB2-based junctions. The gap functions in different bands in MgB2 are obtained from an extended Eliashberg formalism, using the results of band structure calculations. The temperature and angle dependencies of MgB2 tunneling spectra and the Josephson critical current are calculated. The conditions for observing one or two gaps are given. We argue that the model may help to settle the current debate concerning two-band superconductivity in MgB2.
270 citations
TL;DR: In this paper, the Eliashberg equations were solved for both an isotropic one-band model and a twoband model with different superconducting gaps on the π-band and σ-band Fermi surfaces.
Abstract: The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB2 is compared to first-principles calculations with the Coulomb repulsion, µ*, as the only parameter which is fixed to give the measured Tc. We solve the Eliashberg equations for both an isotropic one-band model and a two-band model with different superconducting gaps on the π-band and σ-band Fermi surfaces. The agreement with experiments is considerably better for the two-band model than for the one-band model.
259 citations
TL;DR: In this paper, the results of first-principles calculations of the electronic structure and the electron-phonon interaction in MgB2 are used to study theoretically the temperature dependence and anisotropy of the magnetic-field penetration depth.
Abstract: The results of first-principles calculations of the electronic structure and the electron-phonon interaction in MgB2 are used to study theoretically the temperature dependence and anisotropy of the magnetic-field penetration depth. The effects of impurity scattering are essential for a proper description of the experimental results. We compare our results with experimental data and we argue that the two-band model describes the data rather well.
145 citations
Posted Content•
TL;DR: In this article, Choi et al. pointed out that variation of the superconducting gap inside the sigma- or the pi-bands can hardly be observed in real samples, and taking the anisotropy of the Coulomb repulsion into account influences the size of the small gap, Delta_pi.
Abstract: Choi et al. [Phys. Rev. B 66, 020513 (2002)] recently presented first principles calculations of the electron-phonon coupling and superconductivity in MgB2, emphasizing the importance of anisotropy and anharmonicity. We point out that (1) variation of the superconducting gap inside the sigma- or the pi-bands can hardly be observed in real samples, and (2) taking the anisotropy of the Coulomb repulsion into account influences the size of the small gap, Delta_pi.
35 citations
TL;DR: In this paper, the electronic structure calculations of a noncollinear multiple spin-density-wave (MSDW) state in γ-Fe, which was found in a recent molecular-dynamics calculation, have been performed on the basis of the first-principlestight-binding linear muffin-tin orbital method and the generalized gradient approximation potential.
Abstract: The electronic structure calculations of a noncollinear multiple spin-density-wave (MSDW) state in γ-Fe, which was found in a recent molecular-dynamics calculation, have been performed on the basis of the first-principlestight-binding linear muffin-tin orbital method and the generalized gradient approximation potential. The calculated MSDW state is shown to be dominated by 3 Q waves with wave number Q = 0.6 in units of 2π/a, a being the fcc lattice constant. The secondary waves are created so as to suppress the amplitude fluctuations of local magnetic moments. It is found that the energy of the MSDW state is lower than that of the single-Q helical state with Q = 0.6 at any volume due to the dip of the density of states at the Fermi level. From the energy comparison of various magnetic structures, it is concluded that the MSDW state may be stabilized in the region 6.8
16 citations
TL;DR: In this article, the Anderson impurity model was used to fit the shape of the main lines, obtaining good agreement with the data from Nd 2 CuO 4, while the energy spread of the two screening channels (local and nonlocal) is well reproduced, the theory underestimates the width of the non-local screened feature.
Abstract: We have studied the core level photoemission spectra of the two-dimensional cuprates Sr 2 CuO 2 Cl 2 , Sr 2 CuO 2 Br 2 . Ca 2 CuO 2 Cl 2 . Bi 2 Sr 2 CaCu 2 O 8 + Φ , and Nd 2 CuO 4 , with particular focus on the screening response to core-hole creation in the Cu-2p 3 / 2 level. The influence of the apex positions on the shape of the so-called main line is investigated, and found to be weak. Additionally, an Anderson impurity model was used to fit the shape of the main lines, obtaining good agreement with the data from Nd 2 CuO 4 . For the other compounds, while the energy spread of the two screening channels (local and nonlocal) is well reproduced, the theory underestimates the width of the nonlocally screened feature. The shapes of the main lines are discussed in detail.
11 citations
TL;DR: In this paper, it was shown that the contact field at the Cu site (CuO2-plane) is controlled essentially by the energy of the so-called axial-orbital, a hybrid between Cu 4s, apical Ocpz and farther orbitals e.g. on La or Hg.
Abstract: We show that, in hole-doped superconductors, the contact field at Cu site (CuO2-plane) is controlled essentially by the energy of the so-called axial–orbital, a hybrid between Cu 4s, apical Ocpz and farther orbitals e.g. on La or Hg. As an example, we analyze in full detail the case of HgBa2CuO4. Consequences for the electronic structure of cuprates are analyzed.
1 citations