Hydrostatic Pressure-enhanced correlated magnetism and Chern insulator in moir'e WSe2

TL;DR

This study demonstrates that hydrostatic pressure can reversibly tune correlated magnetic and topological phases in twisted bilayer WSe2, revealing a transition from a Chern insulator to a Mott insulator with enhanced moiré potential.

Contribution

We introduce a cryogenic dual-gated diamond-anvil platform for hydrostatic pressure tuning in twisted bilayer WSe2, enabling exploration of pressure-induced correlated and topological phase transitions.

Findings

Pressure enhances moiré potential and stabilizes ferromagnetism.

Observation of a topological phase transition from Chern insulator to Mott insulator at ~2 GPa.

First-principles calculations show a Gamma-to-K valence-band switching drives the transition.

Abstract

Moir\'e semiconductors offer flat bands where Coulomb interactions and band topology intertwine, while interlayer coupling plays a central role in forming the moir\'e potential. However, limited interlayer coupling strength and the lack of efficient tuning methods hinder further exploration of correlated phenomena in moir\'e semiconductors. Here we introduce a cryogenic dual-gated diamond-anvil platform using helium as a pressure medium, enabling reversible hydrostatic tuning together with magneto-optical spectroscopy in twisted bilayer WSe2. Pressure enhances the moir\'e potential, redshifts excitons, and stabilizes Stoner ferromagnetism otherwise absent at a 3.1-degree twist. Simultaneously, the half-filled C = 1 Chern insulating state strengthens, exhibiting a reduced saturation field. Moreover, we observe a topological phase transition from a Chern insulator to a Mott insulator at around 2 GPa. First-principles calculations reveal that a Gamma-to-K valence-band-maximum switching drives this transition by converting an Ising-like topological K-valley miniband into a spin-degenerate trivial Gamma miniband. Our findings demonstrate hydrostatic pressure as a powerful, continuous control axis for correlated magnetism and topological band engineering in moir\'e materials.