Pseudo-gap in tunneling spectra as a signature of inhomogeneous superconductivity in oxide interfaces

TL;DR

This paper proposes a model for the pseudo-gap observed at LaAlO3/SrTiO3 interfaces, attributing it to inhomogeneous superconductivity with superconducting islands embedded in a metallic background, explaining tunneling spectra features.

Contribution

It introduces a theoretical framework for inhomogeneous superconductivity at oxide interfaces, linking local superconducting islands to observed tunneling spectra and pseudo-gap phenomena.

Findings

Tunneling spectra show suppression of density of states above the percolation temperature.

Superconducting islands have BCS-like properties with randomly distributed critical temperatures.

Proximity effect induces superconductivity in the metallic background at lower temperatures.

Abstract

We present a theory for the pseudo-gap state recently observed at the LaAlO3/SrTiO3 interface, based on superconducting islands embedded in a metallic background. Superconductivity within each island is BCS-like, and the local critical temperatures are randomly distributed, some of them necessarily exceeding the critical temperature for global percolation to the zero resistance state. Consequently, tunneling spectra display a suppression of the density of states and coherence peaks already well above the percolative transition. This model of inhomogeneous superconductivity accounts well for the experimental tunneling spectra. The temperature dependence of the spectra suggests that a sizable fraction of the metallic background becomes superconducting by proximity effect when the temperature is lowered.