Unconventional Metallicity and Giant Thermopower in a Strongly Interacting Two Dimensional Electron System

TL;DR

This study reveals unexpected metallic thermopower behavior in strongly localized low-density 2D electron systems, suggesting a new quantum state influenced by strong Coulomb interactions.

Contribution

It uncovers anomalously large thermopower in a regime where traditional theories predict insulating behavior, indicating a novel quantum state in dilute 2DESs.

Findings

Thermopower decreases linearly with temperature even in high-resistance regimes.

Thermopower magnitude exceeds non-interacting predictions by over two orders.

Evidence suggests a new quantum state with strong electron interactions.

Abstract

We present thermal and electrical transport measurements of low-density (10$^{14}$ m$^{-2}$), mesoscopic two-dimensional electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures. We find that even in the supposedly strongly localised regime, where the electrical resistivity of the system is two orders of magnitude greater than the quantum of resistance $h/e^2$, the thermopower decreases linearly with temperature indicating metallicity. Remarkably, the magnitude of the thermopower exceeds the predicted value in non-interacting metallic 2DESs at similar carrier densities by over two orders of magnitude. Our results indicate a new quantum state and possibly a novel class of itinerant quasiparticles in dilute 2DESs at low temperatures where the Coulomb interaction plays a pivotal role.