Hidden Order as a Source of Interface Superconductivity

TL;DR

This paper proposes a universal mechanism for interfacial superconductivity driven by the suppression of competing hidden orders at interfaces, explaining localized superconductivity in various heterostructures through a Ginzburg--Landau framework.

Contribution

It introduces a general theory linking interface-induced suppression of competing orders to local superconductivity using Ginzburg--Landau equations.

Findings

Superconductivity localizes near interfaces due to order suppression.

Quantized temperature and doping levels for superconductivity emergence.

Surface superconductivity can occur even with minimal suppression of competing order.

Abstract

Interfacial superconductivity is observed in a variety of heterostructures composed of different materials including superconducting and nonsuperconducting (at appropriate doping and temperatures) cuprates and iron-based pnictides. The origin of this superconductivity remains in many cases unclear. Here, we propose a general mechanism of interfacial superconductivity for systems with competing order parameters. We assume that parameters characterizing the material allow formation of another order like charge- or spin-density wave competing and prevailing superconductivity in the bulk (hidden superconductivity). Diffusive electron scattering on the interface results in a suppression of this order and releasing the superconductivity. Our theory is based on the use of Ginzburg--Landau equations applicable to a broad class of systems. We demonstrate that the local superconductivity appears in the vicinity of the interface and the spatial dependence of the superconducting order parameter~$\Delta(x)$ is described by the Gross--Pitaevskii equation. Solving this equation we obtain quantized values of temperature and doping levels at which~$\Delta(x)$ appears. Remarkably, the local superconductivity shows up even in the case when the rival order is only slightly suppressed and may arise also on the surface of the sample (surface superconductivity).