Anisotropic, two-dimensional, disordered Wigner solid

TL;DR

This paper reports experimental evidence of an anisotropic, disordered 2D Wigner solid formed at very low electron densities in a clean, anisotropic electron system, revealing nonlinear and anisotropic transport characteristics.

Contribution

First experimental observation of an anisotropic, disordered 2D Wigner solid in a low-disorder, anisotropic electron system at extremely low densities.

Findings

Nonlinear current-voltage characteristics at high r_s values.

Anisotropic voltage thresholds in the nonlinear regime.

Evidence of a pinned, disordered Wigner solid.

Abstract

The interplay between the Fermi sea anisotropy, electron-electron interaction, and localization phenomena can give rise to exotic many-body phases. An exciting example is an anisotropic two-dimensional (2D) Wigner solid (WS), where electrons form an ordered array with an anisotropic lattice structure. Such a state has eluded experiments up to now as its realization is extremely demanding: First, a WS entails very low densities where the Coulomb interaction dominates over the kinetic (Fermi) energy. Attaining such low densities while keeping the disorder low is very challenging. Second, the low-density requirement has to be fulfilled in a material that hosts an anisotropic Fermi sea. Here, we report transport measurements in a clean (low-disorder) 2D electron system with anisotropic effective mass and Fermi sea. The data reveal that at extremely low electron densities, when the r_s parameter, the ratio of the Coulomb to the Fermi energy, exceeds 38, the current-voltage characteristics become strongly nonlinear at small dc biases. Several key features of the nonlinear characteristics, including their anisotropic voltage thresholds, are consistent with the formation of a disordered, anisotropic WS pinned by the ubiquitous disorder potential.