High-temperature superconductivity and the characteristics of the electronic energy spectrum

Abstract

We exhibit, for arbitrary time variations of the parameters of the generalised harmonic oscillator Hamiltonian, a canonical transformation which facilitates an exact analysis of quantal phase and classical angle. Formulae for Berry's phase and Hannay's angle are readily obtained by taking the adiabatic limit of the exact theory.

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

“…Moreover the effective repulsive Coulomb pseudopotential in the Migdal Eliasberg theory goes to zero (so the effective coupling strength increases) where the interband pairing is dominant. A particular case of multiband superconductivity is where a Van Hove-Lifshits feature [191] in the electronic energy spectrum within the energy window of the pairing interaction is taken into account [32,62] and it is similar to consider in anisotropic superconductivity the Van Hove singularity in a hot spot in the k-space as it occurs at antinodal points in cuprate superconductors.…”

The theory of thermodynamic and magnetic properties of multi-band superconductors

“…Using the two-band model and assuming the moderate values of the coupling constants, one can obtain high values of T c , the two energy gaps 2∆ 1 /T c > 3.5 and 2∆ 2 /T c < 3.5, large negative values dlnT c /dlnV (V is the volume), positive curvature of the upper critical field near the transition temperature, etc. [34][35][36][37][38]. Furthermore, in the two-band model, it is possible to describe the decrease of T c with increasing system disorder [39][40][41].…”

“…[34][35][36][37][38]. Furthermore, in the two-band model, it is possible to describe the decrease of T c with increasing system disorder [39][40][41].…”

“…A particular interest is attached to the possibility to obtain a bell-shaped dependence of T c and of the jump of heat capacity (C S − C N )/C N at the point T = T c on the carrier density [41,42,44]. In the three-band model, it is possible to obtain a "step" in the dependence of T c on the carrier density [45,46].…”

“…In the three-band model, it is possible to obtain a "step" in the dependence of T c on the carrier density [45,46]. The investigation of the properties of superconductors with overlapping energy bands on the Fermi surface and the electronic topological transitions was reviewed in [47]. This review contains the classical results of the problem.…”