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

Abstract

The phenomenon of field-induced superconductor-to-insulator transitions observed experimentally in electron-doped SrTiO$_{3}$/LaAlO$_{3}$ interfaces, analyzed recently by means of 2D superconducting fluctuations theory (Phys. Rev. B \textbf{104}, 054503 (2021)), is revisited with new insights associating it with the appearance at low temperatures of field-induced boson insulating states. Within the framework of the time-dependent Ginzburg-Landau functional approach, we pinpoint the origin of these states in field-induced extreme softening of fluctuation modes over a large region in momentum space, upon diminishing temperature, which drives Cooper-pair fluctuations to condense into mesoscopic puddles in real space. Dynamical quantum tunneling of Cooper-pair fluctuations out of these puddles, introduced within a phenomenological approach, which break into mobile single-electron states, contains the high-field resistance onset predicted by the exclusive boson theory.