The Ginzburg-Landau theory is presented for a two-band superconductor with emphasis on MgB2. Experiments are proposed which lead to identification of the possible scenarios: whether both σand π-bands superconduct or σ-alone. According to the second scenario a microscopic theory of superconducting MgB2 is proposed based on the strongly interacting σ-electrons and non-correlated π-electrons of bo...

By interpreting various experimental data for the new high temperature FeAs type superconductors in terms of lattice mediated multigap superconductivity, it is shown that these systems strongly resemble MgB2, however, with the distinction that local polaronic lattice effects exist. This fact establishes a connection to cuprate high temperature superconductors where polaron formation is essentia...

The effects of the precursor milling energy on the superconducting and microstructural homogeneity of Fe-sheathed MgB2 monocore wires and tapes have been investigated. The conductors were produced by the powder-in-tube method using drawing and rolling deformation methods and in situ reaction. Combined magnetooptical, structural and magnetization measurements were performed on MgB2 superconducti...

A sharp collective charge excitation is predicted in MgB2 at approximately 2.5 eV for q perpendicular to the boron layers, based on an all-electron analysis of the dynamical density response within time-dependent density functional theory. This novel excitation, consisting of coherent charge fluctuation between Mg and B sheets, induces an abrupt plasma edge in the experimentally observable refl...

We present a first principles investigation of the lattice dynamics and electron-phonon coupling of the superconductor MgB2 and the isostructural AlB2 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. Complete phonon dispersion curves and Eliashberg functions alpha2F are calculated for both systems. The main differences are related to hig...

Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate...

In the fall of 2001, a group of researchers at Aoyama Gakuin University published a report in Nature on a new superconducting material, MgB2 (magnesium boride), which has a critical temperature of 39 K [1], the finding of which sent shock waves around the world. The discovery of superconductivity in Hg traces back to 1911. Since then, various metals and metal compounds have been confirmed to sh...

Tunneling data on magnesium diboride, MgB2, are reviewed with a particular focus on superconductor–insulator–superconductor (SIS) junctions formed by a break–junction method. The collective tunneling literature reveals two distinct energy scales, a large gap, ∆L ∼ 7.2 meV, close to the expected BCS value, and a small gap, ∆S ∼ 2.4 meV. The SIS break junctions show clearly that the small gap clo...

We present a first principles investigation of the lattice dynamics and electron-phonon coupling of the superconductor MgB2 and the isostructural AlB2 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. Complete phonon dispersion curves and Eliashberg functions αF are calculated for both systems. We also report on Raman measurements, which ...