Surface superconductor-insulator transition induced by an electric field

TL;DR

This paper investigates how an electric field can induce a transition from superconducting to insulating states on the surface of a bulk superconductor, revealing a phase diagram with potential experimental relevance.

Contribution

It introduces a theoretical study of surface phase transitions under electric fields using Bogoliubov-de Gennes equations, extending understanding of electric field effects on bulk superconductor surfaces.

Findings

Surface insulating states occur at high electric fields.

Phase diagram includes superconducting, metallic, and insulating regimes.

Results align qualitatively with experimental measurements on thin flakes.

Abstract

It is well-known that the electric field can induce phase transitions between superconducting, metallic and insulating states in thin-film materials due to its control of the charge carrier density. Since a similar effect on the charge carriers can also be expected for surfaces of bulk samples, here we investigate the transformation of the surface states in a superconductor under an applied screened electric field. Our study is performed by numerically solving the self-consistent Bogoliubov-de Gennes equations for the one-dimensional attractive Hubbard model. It is found that the surface insulating regime occurs at sufficiently large (but still experimentally accessible) electric fields. Our calculations yield the phase diagram of the surface superconducting, metallic, and insulating states for a wide range of temperatures and applied fields. Our results are in qualitative agreement with the phase diagram obtained by the transport measurements for (Li, Fe)OHFeSe thin flakes [Sci. Bull. 64, 653 (2019); ACS Nano 14, 7513 (2020)].