Effect of multiband transport on charge carrier density fluctuations at the LaAlO$_3$/SrTiO$_3$ interface

TL;DR

This study investigates how multiband transport influences charge carrier fluctuations at the LaAlO₃/SrTiO₃ interface, revealing a gate-tunable Lifshitz transition and distinct noise characteristics linked to interband scattering.

Contribution

It provides detailed experimental evidence of multiband effects and interband scattering in LaAlO₃/SrTiO₃, demonstrating resistance fluctuation spectroscopy as a tool to probe charge dynamics across a Lifshitz transition.

Findings

Identification of a gate-tunable Lifshitz transition.

Different noise mechanisms below and above the transition.

Evidence of interband scattering affecting transport properties.

Abstract

Multiband transport in superconductors is interesting both from an academic as well as an application point of view. It has been postulated that interband scattering can significantly affect the carrier dynamics in these materials. In this article we present a detailed study of the electrical transport properties of the high-mobility two-dimensional electron gas residing at the interface of LaAlO$_3$/SrTiO$_3$, a prototypical multi-band superconductor. We show, through careful measurements of the gate dependence of the magnetoresistance and resistance fluctuations at ultra-low temperatures, that transport in the superconducting regime of this system has contributions from two bands which host carriers of very different characters. We identify a gate-voltage tunable Lifshitz transition in the system and show that the resistance fluctuations have strikingly different features on either side of it. At low carrier densities, resistance noise is dominated by number-density fluctuations arising from trapping-detrapping of charge carriers from defects in the underlying SrTiO$_3$ substrate, characteristic of a single-band semiconductor. Above the Lifshitz transition, the noise presumably originates from inter-band scattering. Our work highlights the importance of inter-band scattering processes in determining the transport properties of low-dimensional systems and projects resistance fluctuation spectroscopy as a viable technique for probing the charge carrier dynamics across a Lifshitz transition.