Signatures of bilayer Wigner crystals in a transition metal dichalcogenide heterostructure

TL;DR

This paper reports the experimental observation of bilayer Wigner crystals in atomically thin MoSe2 heterostructures without magnetic fields, revealing stable correlated insulating states and phase transitions at cryogenic temperatures.

Contribution

It demonstrates the formation of bilayer Wigner crystals in MoSe2 bilayers through optical signatures, a novel achievement in 2D semiconductors without external magnetic or confinement fields.

Findings

Observation of correlated insulating states at specific electron doping levels.

Identification of stable bilayer Wigner crystal phases stabilized by inter-layer interactions.

Detection of quantum and thermal melting transitions at cryogenic temperatures.

Abstract

A Wigner crystal, a regular electron lattice arising from strong correlation effects, is one of the earliest predicted collective electronic states. This many-body state exhibits quantum and classical phase transitions and has been proposed as a basis for quantum information processing applications. In semiconductor platforms, two-dimensional Wigner crystals have been observed under magnetic field or moir\'e-based lattice potential where the electron kinetic energy is strongly suppressed. Here, we report bilayer Wigner crystal formation without a magnetic or confinement field in atomically thin MoSe$_2$ bilayers separated by hexagonal boron nitride. We observe optical signatures of robust correlated insulating states formed at symmetric (1:1) and asymmetric (4:1 and 7:1) electron doping of the two MoSe$_2$ layers at cryogenic temperatures. We attribute these features to the bilayer Wigner crystals formed from two commensurate triangular electron lattices in each layer, stabilized via inter-layer interaction. These bilayer Wigner crystal phases are remarkably stable and undergo quantum and thermal melting transitions above a critical electron density of up to $6 \times10^{12}$ cm$^{-2}$ and at temperatures of ~40 K. Our results demonstrate that atomically thin semiconductors provide a promising new platform for realizing strongly correlated electronic states, probing their electronic and magnetic phase transitions, and developing novel applications in quantum electronics and optoelectronics.