Superconducting Bands Stabilizing Superconductivity in YBa2Cu3O7 and MgB2

MgB2: superconductivity and pressure effects

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...

Nonadiabatic polaronic superconductivity in MgB2 and cuprates

Strongly interacting σ-electrons and MgB2 superconductivity

MgB(pnpn ) 2 is classified as a system with strongly interacting σelectrons and non-correlated π-electrons of boron ions. The kinematic and Coulomb interaction V between the orbitally degenerated σ-electrons provide the superconducting state with an anisotropic gap of s*-wave symmetry. The critical temperature Tc has a non-monotonic dependence on the distance r between the centers of gravity of...

Origin of superconductivity transition broadening in MgB2

We report resistivity and magnetization of single crystal MgB2, focusing on the broadening of superconducting (SC) transition in magnetic fields. In-plane and outof-plane resistivity indicate that the broadening of superconducting transition is independent of Lorentz force and that it is merely dependent on the magnetic field direction. In magnetization, diamagnetic signal begins to appear at a...

Superconductivity in MgB2: clean or dirty?

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 u...