Stripe phases in WSe2/WS2 moir\'e superlattices

TL;DR

This paper reports the discovery and characterization of stripe phases in WSe2/WS2 moiré superlattices, revealing their tunability and connection to theoretical models, and highlighting their significance in understanding correlated electronic states.

Contribution

It provides the first experimental observation of stripe phases in 2D semiconductor moiré superlattices with tunable charge densities, linking experimental results to theoretical phase diagrams.

Findings

Stripe phases are observed at specific fillings, notably 1/2, 1/4, 2/5, 3/5.

The 1/2 state is an incompressible stripe crystal phase.

Stripe phases can be melted by thermal fluctuations around 35 K.

Abstract

Stripe phases, in which the rotational symmetry of charge density is spontaneously broken, occur in many strongly correlated systems with competing interactions. One representative example is the copper-oxide superconductors, where stripe order is thought to be relevant to the mechanism of high-temperature superconductivity. Identifying and studying the stripe phases in conventional strongly correlated systems are, however, challenging due to the complexity and limited tunability of these materials. Here we uncover stripe phases in WSe2/WS2 moir\'e superlattices with continuously gate-tunable charge densities by combining optical anisotropy and electronic compressibility measurements. We find strong electronic anisotropy over a large doping range peaked at 1/2 filling of the moir\'e superlattice. The 1/2-state is incompressible and assigned to a (insulating) stripe crystal phase. It can be continuously melted by thermal fluctuations around 35 K. The domain configuration revealed by wide-field imaging shows a preferential alignment along the high-symmetry axes of the moir\'e superlattice. Away from 1/2 filling, we observe additional stripe crystals at commensurate filling 1/4, 2/5 and 3/5. The anisotropy also extends into the compressible regime of the system at incommensurate fillings, indicating the presence of electronic liquid crystal states. The observed filling-dependent stripe phases agree with the theoretical phase diagram of the extended Hubbard model on a triangular lattice in the flat band limit. Our results demonstrate that two-dimensional semiconductor moir\'e superlattices are a highly tunable platform to study the stripe phases and their interplay with other symmetry breaking ground states.