Optical detection of Mott and generalized Wigner crystal states in WSe2/WS2 moir\'e superlattices

TL;DR

This paper demonstrates optical detection of Mott and Wigner crystal states in WSe2/WS2 moiré superlattices, revealing strongly correlated phases and long-lived spin excitations, expanding understanding of correlated physics in TMDC heterostructures.

Contribution

The study introduces an optical method to identify correlated insulating states and fractional fillings in TMDC moiré superlattices, revealing new correlated phenomena beyond graphene.

Findings

Detection of Mott insulator at one hole per site.

Observation of fractional filling insulating phases at 1/3 and 2/3.

Identification of microsecond-long spin relaxation in the Mott state.

Abstract

Moir\'e superlattices are emerging as a new route for engineering strongly correlated electronic states in two-dimensional van der Waals heterostructures, as recently demonstrated in the correlated insulating and superconducting states in magic-angle twisted bilayer graphene and ABC trilayer graphene/boron nitride moir\'e superlattices. Transition metal dichalcogenide (TMDC) moir\'e heterostructures provide another exciting model system to explore correlated quantum phenomena, with the addition of strong light-matter interactions and large spin-orbital coupling. Here we report the optical detection of strongly correlated phases in semiconducting WSe2/WS2 moir\'e superlattices. Our sensitive optical detection technique reveals a Mott insulator state at one hole per superlattice site ({\nu} = 1), and surprising insulating phases at fractional filling factors {\nu} = 1/3 and 2/3, which we assign to generalized Wigner crystallization on an underlying lattice. Furthermore, the unique spin-valley optical selection rules of TMDC heterostructures allow us to optically create and investigate low-energy spin excited states in the Mott insulator. We reveal an especially slow spin relaxation lifetime of many microseconds in the Mott insulating state, orders-of-magnitude longer than that of charge excitations. Our studies highlight novel correlated physics that can emerge in moir\'e superlattices beyond graphene.