Strain and ferroelectric soft mode induced superconductivity in strontium titanate

TL;DR

This paper explores how strain influences superconductivity in SrTiO₃, predicting increased critical temperatures and altered carrier density ranges due to ferroelectric soft mode effects, with a theoretical Ginzburg-Landau model elucidating strain dependencies.

Contribution

It introduces a theoretical framework linking strain-induced ferroelectric soft modes to enhanced superconductivity in SrTiO₃, including predictions of critical temperature shifts and strain-dependent behaviors.

Findings

Critical temperature increases with tensile strain.

Superconducting dome shifts to lower carrier densities.

Linear dependence of Tc on strain in a 2D Ginzburg-Landau model.

Abstract

We investigate the effects of strain on superconductivity with particular reference to SrTiO$_3$. Assuming that a ferroelectric mode that softens under tensile strain is responsible for the coupling, an increase in the critical temperature and range of carrier densities for superconductivity is predicted, while the peak of the superconducting dome shifts towards lower carrier densities. Using a Ginzburg-Landau approach in 2D, we find a linear dependence of the critical temperature on strain: if the couplings between the order parameter and strains in different directions differ while their sum is fixed, different behaviours under uniaxial and biaxial (uniform) strain can be understood.