Dielectric catastrophe at the Wigner-Mott transition in a moiré superlattice

Abstract

The bandwidth-tuned Wigner-Mott transition is an interaction-driven phase transition from a generalized Wigner crystal to a Fermi liquid. Because the transition is generally accompanied by both magnetic and charge-order instabilities, it remains unclear if a continuous Wigner-Mott transition exists. Here, we demonstrate bandwidth-tuned metal-insulator transitions at fixed fractional fillings of a MoSe ₂/WS ₂ moiré superlattice. The bandwidth is controlled by an out-of-plane electric field. The dielectric response is probed optically with the 2s exciton in a remote WSe ₂ sensor layer. The exciton spectral weight is negligible for the metallic state with a large negative dielectric constant. It continuously vanishes when the transition is approached from the insulating side, corresponding to a diverging dielectric constant or a ‘dielectric catastrophe’ driven by the critical charge dynamics near the transition. Our results support the scenario of continuous Wigner-Mott transitions in two-dimensional triangular lattices and stimulate future explorations of exotic quantum phases in their vicinities.

Abstract

The Wigner-Mott insulator is driven by extended Coulomb repulsion, rather than the on-site Coulomb repulsion of the Mott insulator. Here, the authors observe a continuous bandwidth-tuned transition between a metal and a Wigner-Mott insulator in a MoSe ₂/WS ₂ moiré superlattice at fractional lattice filling.