On the origin of Field-Induced Boson Insulating States in a 2D Superconducting Electron Gas with Strong Spin-Orbit Scatterings

TL;DR

This paper investigates the origin of field-induced insulating states in 2D superconducting electron gases with strong spin-orbit coupling, revealing that fluctuation-driven divergence leads to Boson insulators at high magnetic fields.

Contribution

It introduces a model explaining the transition to Boson insulating states via fluctuation mass divergence in 2D electron gases with strong spin-orbit scatterings, extending previous fluctuation theories.

Findings

High-field Boson insulator states driven by fluctuation mass divergence.

Enhanced magnetoresistance at high fields in low carrier density systems.

Dynamical quantum tunneling prevents divergence at zero temperature.

Abstract

We search for the deep origin of the field-induced superconductor-to-insulator transitions observed experimentally in electron-doped SrTiO$_{3}$/LaAlO$_{3}$ interfaces, which were analyzed theoretically very recently within the framework of superconducting fluctuations approach (Phys. Rev. B $\bf{104}$, 054503 (2021)). Employing the 2D electron-gas model with strong spin-orbit scatterings, we have found that in the zero temperature limit, field-induced unbounded growth of the fluctuation mass, and consequent divergence of Cooper-pair density in mesoscopic puddles, drives the system to Boson insulating states at high fields. Application of this model to the gate-voltage tuned 2D electron system, created in the SrTiO$_{3}$/LaAlO$_{3}$ (111) interface at low temperatures, shows that, at sufficiently high fields, the DOS conductivity prevails over the paraconductivity, resulting in strongly enhanced magnetoresistance in systems with sufficiently small carriers density. Dynamical quantum tunneling of Cooper pairs breaking into mobile normal-electrons states, which prevent the divergence at zero temperature, contain the high-field resistance onset.