Effect of multiband transport on charge carrier density fluctuations at the LaAlO3/SrTiO3 interface

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 LaAlO3/SrTiO3, a prototypical multiband superconductor. We show, through careful measurements of the gate dependence of the magnetoresistance and resistance fluctuations at ultralow 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 SrTiO3 substrate, characteristic of a single-band semiconductor. Above the Lifshitz transition, the noise presumably originates from interband scattering. Our paper highlights the importance of interband 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.