Unconventional dynamical covalency driven superconductivity in Nb doped SrTiO3

TL;DR

This paper reveals that Nb-doped SrTiO3 exhibits highly unconventional multiband superconductivity driven by anisotropic interactions and soft modes, with unique temperature-dependent properties distinct from typical superconductors.

Contribution

It demonstrates the unconventional nature of superconductivity in Nb-doped SrTiO3, highlighting the role of anisotropic interactions and soft modes in its two-gap behavior.

Findings

The smaller superconducting gap follows a non-BCS temperature dependence.

The superfluid density shows an inflection point near Tc, unlike typical superconductors.

Unconventional multiband superconductivity driven by covalency effects.

Abstract

Nb doped SrTiO3, the first discovered two-gap superconductor, is shown to be the most unconventional one of the known multiband superconductors, since the smaller of the two superconducting gaps follows a non BCS temperature dependence. Such a behavior stems from two cooperating effects: an extreme anisotropy in the frequency dependent interactions, involving one very soft mode and an almost vanishing interband interaction. In contrast to all other multiband superconductors, the temperature dependence of the superfluid density of Nb doped SrTiO3 is predicted to exhibit an inflection point close to Tc and not close to T=0.