Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO$_{3}$/SrTiO$_{3}$/SmTiO$_{3}$ Quantum Well Structures

TL;DR

This study investigates low-temperature voltage fluctuations in mesoscopic SmTiO$_{3}$/SrTiO$_{3}$/SmTiO$_{3}$ quantum wells, revealing mesoscopic effects and potential quantum coherence phenomena that influence transport properties in strongly correlated oxide interfaces.

Contribution

It reports novel low-temperature voltage fluctuations in mesoscopic oxide heterostructures and proposes a mechanism involving mesoscopic Seebeck coefficient fluctuations, advancing understanding of quantum transport in these systems.

Findings

Voltage fluctuations grow below 20 K and are suppressed by larger contacts.

Magnetoresistance fluctuations suggest mesoscopic quantum effects.

Transport properties can be tuned from Fermi-liquid to non-Fermi-liquid regimes.

Abstract

Heterointerfaces of SrTiO$_{3}$ with other transition metal oxides make up an intriguing family of systems with a bounty of coexisting and competing physical orders. Some examples, such as LaAlO$_{3}$/SrTiO$_{3}$, support a high carrier density electron gas at the interface whose electronic properties are determined by a combination of lattice distortions, spin-orbit coupling, defects, and various regimes of magnetic and charge ordering. Here, we study electronic transport in mesoscale devices made with heterostructures of SrTiO$_{3}$ sandwiched between layers of SmTiO$_{3}$, in which the transport properties can be tuned from a regime of Fermi-liquid like resistivity ($\rho \sim T^{2}$) to a non-Fermi liquid ($\rho \sim T^{5/3}$) by controlling the SrTiO$_{3}$ thickness. In mesoscale devices at low temperatures, we find unexpected voltage fluctuations that grow in magnitude as $T$ is decreased below 20 K, are suppressed with increasing contact electrode size, and are independent of the drive current and contact spacing distance. Magnetoresistance fluctuations are also observed, which are reminiscent of universal conductance fluctuations but not entirely consistent with their conventional properties. Candidate explanations are considered, and a mechanism is suggested based on mesoscopic temporal fluctuations of the Seebeck coefficient. An improved understanding of charge transport in these model systems, especially their quantum coherent properties, may lead to insights into the nature of transport in strongly correlated materials that deviate from Fermi liquid theory.