Enhanced Superconducting Transition Temperature due to Tetragonal Domains in Two-Dimensionally Doped SrTiO$_3$

TL;DR

This study reveals that tetragonal domains in niobium-doped SrTiO$_3$ significantly enhance local superconducting transition temperatures, highlighting the role of structural domains and dielectric anisotropy in its superconductivity mechanism.

Contribution

It demonstrates the impact of twin domain structures on local $T_c$ in SrTiO$_3$, emphasizing the importance of dielectric anisotropy in understanding its superconductivity.

Findings

Regions with higher $T_c$ correlated with twin domain patterns

Superconducting transition temperature increased by over 10% in certain domains

Structural domains influence local superconducting properties

Abstract

Strontium titanate is a low-temperature, non-Bardeen-Cooper-Schrieffer superconductor that superconducts to carrier concentrations lower than in any other system and exhibits avoided ferroelectricity at low temperatures. Neither the mechanism of superconductivity in strontium titanate nor the importance of the structure and dielectric properties for the superconductivity are well understood. We studied the effects of twin structure on superconductivity in a 5.5-nm-thick layer of niobium-doped SrTiO$_{3}$ embedded in undoped SrTiO$_{3}$. We used a scanning superconducting quantum interference device susceptometer to image the local diamagnetic response of the sample as a function of temperature. We observed regions that exhibited a superconducting transition temperature $T_{c}$ $\gtrsim$ 10% higher than the temperature at which the sample was fully superconducting. The pattern of these regions varied spatially in a manner characteristic of structural twin domains. Our results emphasize that the anisotropic dielectric properties of SrTiO$_{3}$ are important for its superconductivity, and need to be considered in any theory of the mechanism of the superconductivity.