Giant Oscillating Thermopower at Oxide Interfaces

TL;DR

This study reveals giant oscillating thermopower at LaAlO3/SrTiO3 interfaces, providing direct evidence of localized states and deepening understanding of charge carrier behavior in oxide heterostructures.

Contribution

It presents the first direct evidence of a localized Anderson tail in the 2D electron liquid at the interface, using thermopower measurements as a probe.

Findings

Record-high negative thermopower values under negative gate voltage.

Oscillations in thermopower correspond to Fermi level crossing localized states.

Identification of a localized Anderson tail in the 2D electron system.

Abstract

Understanding the nature of charge carriers at the LaAlO3/SrTiO3 interface is one of the major open issues in the full comprehension of the charge confinement phenomenon in oxide heterostructures. Here, we investigate thermopower to study the electronic structure in LaAlO3/SrTiO3 at low temperature as a function of gate field. In particular, under large negative gate voltage, corresponding to the strongly depleted charge density regime, thermopower displays record-high negative values of the order of 10^4 - 10^5 microV/K, oscillating at regular intervals as a function of the gate voltage. The huge thermopower magnitude can be attributed to the phonon-drag contribution, while the oscillations map the progressive depletion and the Fermi level descent across a dense array of localized states lying at the bottom of the Ti 3d conduction band. This study is the first direct evidence of a localized Anderson tail in the two-dimensional (2D) electron liquid at the LaAlO3/SrTiO3 interface.