Superconducting fluctuations and giant negative magnetoresistance in a gate-voltage tuned two-dimensional electron system with strong spin-orbit impurity scattering

Abstract

We present a quantitative theory of the gate-voltage tuned superconductor-to-insulator transition (SIT) observed experimentally in the 2D electron system created in the (111) interface between crystalline ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ and ${\mathrm{La}\mathrm{Al}\mathrm{O}}_{3}$. Considering two fundamental opposing effects of Cooper-pair fluctuations---the critical conductivity enhancement, known as paraconductivity, and its suppression associated with the loss of unpaired electrons due to Cooper-pairs formation---we generalize the standard thermal fluctuations theory to include interaction between fluctuations within the self-consistent field approximation and quantum tunneling between mesoscopic superconducting puddles within a phenomenological approach. Relying on the quantitative agreement found between our theory and a large body of experimental sheet-resistance data, we conclude that spin-orbit scatterings, via significant enhancement of the interaction between fluctuations, strongly enhance the sheet resistance peak at high fields and reveal anomalous metallic behavior at low fields, due to mixing of relatively heavy electron bands with a light electron band near a Lifshitz point. The large enhancement of the interaction between fluctuations at high fields, where the sheet resistance is strongly amplified, is shown to result in localization of Cooper-pair fluctuations within mesoscopic puddles.