Evidence of Novel Quasiparticles in a Strongly Interacting Two-Dimensional Electron System: Giant Thermopower and Metallic Behaviour

TL;DR

This study reveals evidence of unconventional quasiparticles in a strongly interacting two-dimensional electron system, characterized by giant thermopower and metallic behavior that defy traditional models, suggesting new physics in low-density 2DESs.

Contribution

The paper presents experimental evidence of novel quasiparticles in 2DESs, demonstrated by anomalously large thermopower and unusual resistivity behavior at sub-Kelvin temperatures.

Findings

Thermopower exceeds Mott prediction by over two orders of magnitude.

Resistivity remains high and nearly temperature-independent.

Decoupling and oscillations in thermopower indicate non-electron-like quasiparticles.

Abstract

We report thermopower ($S$) and electrical resistivity ($\rho_{2DES}$) measurements in low-density (10$^{14}$ m$^{-2}$), mesoscopic two-dimensional electron systems (2DESs) in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures. We observe at temperatures $\lesssim$ 0.7 K a linearly growing $S$ as a function of temperature indicating metal-like behaviour. Interestingly this metallicity is not Drude-like, showing several unusual characteristics: i) the magnitude of $S$ exceeds the Mott prediction valid for non-interacting metallic 2DESs at similar carrier densities by over two orders of magnitude; and ii) $\rho_{2DES}$ in this regime is two orders of magnitude greater than the quantum of resistance $h/e^2$ and shows very little temperature-dependence. We provide evidence suggesting that these observations arise due to the formation of novel quasiparticles in the 2DES that are not electron-like. Finally, $\rho_{2DES}$ and $S$ show an intriguing decoupling in their density-dependence, the latter showing striking oscillations and even sign changes that are completely absent in the resistivity.