Multiple nodeless superconducting gaps in optimally-doped SrTi$_{1-x}$Nb$_{x}$O$_{3}$

TL;DR

This study reveals that optimally-doped SrTi$_{1-x}$Nb$_{x}$O$_{3}$ exhibits multiple nodeless superconducting gaps, with thermal conductivity measurements indicating multigap behavior and absence of nodal quasiparticles.

Contribution

First thermal conductivity investigation showing multigap nodeless superconductivity in SrTi$_{1-x}$Nb$_{x}$O$_{3}$ near its maximum T$_{c}$.

Findings

Thermal conductivity deviates from normal state at bulk T$_{c}$ following BRT behavior.

No T-linear term at low temperatures, indicating no nodal quasiparticles.

Field dependence suggests at least two distinct superconducting gaps.

Abstract

We present the first study of thermal conductivity in superconducting SrTi$_{1-x}$Nb$_{x}$O$_{3}$, sufficiently doped to be near its maximum critical temperature. The bulk critical temperature, determined by the jump in specific heat, occurs at a significantly lower temperature than the resistive T$_{c}$. Thermal conductivity, dominated by the electron contribution, deviates from its normal-state magnitude at bulk T$_{c}$, following a Bardeen-Rickayzen-Tewordt (BRT) behavior, expected for thermal transport by Bogoliubov excitations. Absence of a T-linear term at very low temperatures rules out the presence of nodal quasi-particles. On the other hand, the field dependence of thermal conductivity points to the existence of at least two distinct superconducting gaps. We conclude that optimally-doped strontium titanate is a multigap nodeless superconductor.