Imaging Interacting Two-Dimensional Anisotropic Electrons

TL;DR

This study visualizes anisotropic electrons in monolayer ReSe2, revealing an oblique Wigner crystal and its quantum melting, advancing understanding of anisotropic correlated electron phases.

Contribution

First experimental imaging of anisotropic electron wavefunctions and their crystallization in monolayer ReSe2, demonstrating anisotropic Wigner crystal formation and melting behavior.

Findings

Electrons form an oblique Wigner lattice at low density.

Quantum fluctuations induce one-dimensional melting along the light-mass direction.

The resulting phase is a smectic electron liquid crystal.

Abstract

We directly visualize a two-dimensional anisotropic Wigner crystal and its quantum melting in monolayer 1T-ReSe2 using non-invasive scanning tunnelling microscopy. In crystals with anisotropic effective mass, an electron's quantum wavefunction becomes elongated along the light-mass direction to reduce kinetic energy. At low electron density, such anisotropic electrons are predicted to form an oblique Wigner crystal rather than the familiar triangular lattice of isotropic systems. Despite longstanding theoretical interest, this physics has been little explored experimentally. Here we first image the anisotropic shape of individual electrons in gated monolayer ReSe2, whose wavefunctions are strongly elongated along the light-mass direction. At low density, these electrons crystallize into an oblique Wigner lattice. As the density increases, quantum fluctuations grow more rapidly along the light-mass direction than along the heavy-mass direction, driving a one-dimensional melting of the crystal. The resulting state retains order along one direction but melts along the other, consistent with a smectic electron liquid crystal between the electron solid and Fermi liquid phases. Our work establishes monolayer ReSe2 as a platform for studying anisotropic correlated electrons, quantum melting, and coupled one-dimensional electron chains.