Variation in superconducting transition temperature due to tetragonal domains in two-dimensionally doped SrTiO3

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 SrTiO3 embedded in undoped SrTiO3. 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 Tc 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 SrTiO3 are important for its superconductivity, and need to be considered in any theory of the mechanism of the superconductivity.

Large-scale modulation in the superconducting properties of thin films due to domains in theSrTiO3substrate

“…In conducting interfaces with STO, such as LaAlO 3 /SrTiO 3 , the twin structure of STO strongly influences local normal state electronic properties [3][4][5] and weakly modulates the superfluid density in the superconducting state [5]. In δ-doped STO [6][7][8], the twin structure influences the critical temperature [9], T c. In these material systems the current flows either in the STO itself, at an interface with another oxide, or in a doping layer of a few nanometers. The coupling between the STO and the two-dimensional (2D) conducting layer is excellent [10,11].…”

Two-dimensional superconductivity at the (111) LaAlO3/SrTiO3 interface

“…It should be noted that the evolution of a(T ) does not display the characteristic discontinuous jump from a(T + BKT ) = 1 to a(T − BKT ) = 3, but rather transitions smoothly from 1 to 3 over a range of several millikelvin. This behavior, also observed in (001)-and (110)-oriented interfaces [6,22], stems from inhomogeneities in the local superconducting properties of the system (such as inhomogeneous superfluid density [23] or structural twin domains of the STO substrate [24]) which smear the universal jump [25].…”

Correlation between superconductivity, band filling, and electron confinement at the LaAlO3/SrTiO3 interface

“…For SrTiO 3 -based q-2DESs, inhomogeneity due to electronic phase separation is predicted to be an intrinsic property [39,40], depending on an applied gate voltage [40,41]. Another property that can cause inhomogeneity at the surface of SrTiO 3 is tetragonal domain formation with gate voltage, which drives local variations in current density and critical temperature [42][43][44][45].…”