Two-band superconductivity in doped SrTiO$_{3}$ films and interfaces

TL;DR

This study models multi-band superconductivity in doped SrTiO₃ films and interfaces, revealing how doping-induced band occupation enhances transition temperatures and suggesting intra-band pairing dominance, with implications for understanding interface superconductivity.

Contribution

It introduces a two-dimensional two-band model for SrTiO₃, showing how doping affects band occupation and superconductivity, and compares these findings with experimental data to infer pairing mechanisms.

Findings

Doping shifts chemical potential, activating a second band.

Enhanced transition temperature with second band occupation.

Intra-band pairing dominates over inter-band pairing.

Abstract

We investigate the possibility of multi-band superconductivity in SrTiO$_{3}$ films and interfaces using a two-dimensional two-band model. In the undoped compound, one of the bands is occupied whereas the other is empty. As the chemical potential shifts due to doping by negative charge carriers or application of an electric field, the second band becomes occupied, giving rise to a strong enhancement of the transition temperature and a sharp feature in the gap functions, which is manifested in the local density of states spectrum. By comparing our results with tunneling experiments in Nb-doped SrTiO$_{3}$, we find that intra-band pairing dominates over inter-band pairing, unlike other known multi-band superconductors. Given the similarities with the value of the transition temperature and with the band structure of LaAlO$_{3}$/SrTiO$_{3}$ heterostructures, we speculate that the superconductivity observed in SrTiO$_{3}$ interfaces may be similar in nature to that of bulk SrTiO$_{3}$, involving multiple bands with distinct electronic occupations.