Resonant and crossover phenomena in a multiband superconductor tuning the chemical potential near a band edge

TL;DR

This paper investigates resonance phenomena in a two-band superconductor near a band edge, revealing interference effects and gap amplification during a 3D-2D Fermi surface transition, aligning with experimental data.

Contribution

It introduces a detailed analysis of Feshbach-like resonances in multiband superconductors near band edges, highlighting quantum interference effects and gap enhancement.

Findings

Resonances manifest as interference effects in superconducting gaps.

Superconducting gap amplification occurs at the 3D-2D Fermi surface transition.

Results agree with experimental data on honeycomb boron superlattices.

Abstract

Resonances in the superconducting properties, in a regime of crossover from BCS to mixed Bose-Fermi superconductivity, are investigated in a two-band superconductor where the chemical potential is tuned near the band edge of the second mini-band generated by quantum confinement effects. The shape resonances at T=0 in the superconducting gaps (belonging to the class of Feshbach-like resonances) is manifested by interference effects in the superconducting gap at the first large Fermi surface when the chemical potential is in the proximity of the band edge of the second mini-band. The case of a superlattice of quantum wells is considered and the amplification of the superperconducting gaps at the 3D-2D Fermi surface topological transition is clearly shown. The results are found to be in good agreement with available experimental data on a superlattice of honeycomb boron layers intercalated by Al and Mg spacer layers.