Self-Optimized Superconductivity Attainable by Interlayer Phase Separation at Cuprate Interfaces

TL;DR

This paper demonstrates that at cuprate interfaces, superconductivity can be stabilized at optimal levels independent of carrier density, due to interlayer phase separation and self-organization mechanisms, offering new pathways for device design.

Contribution

The study introduces a microscopic model showing that interfaces between a Mott insulator and an overdoped metal pin superconductivity at optimal levels, unlike bulk materials.

Findings

Superconducting amplitude remains at optimal level regardless of carrier concentration.

Interlayer phase separation induces a self-organized electronic structure.

Interfaces can enhance and stabilize superconductivity beyond bulk limitations.

Abstract

Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (e.g. higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, here, we demonstrate that at an interface between a Mott insulator and an overdoped non-superconducting metal, the superconducting amplitude stays always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors, but consistent with the astonishing independence of the critical temperature from the carrier density x observed at interfaces of La2CuO4 and La2-xSrxCuO4. We furthermore identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.