Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices

Abstract

Moiré 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 moiré superlattices 1-4 . Transition metal dichalcogenide (TMDC) moiré heterostructures provide another exciting model system to explore correlated quantum phenomena 5 , 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 moiré superlattices. Our sensitive optical detection technique reveals a Mott insulator state at one hole per superlattice site (ν = 1), and surprising insulating phases at fractional filling factors ν = 1/3 and 2/3, which we assign to generalized Wigner crystallization on an underlying lattice 6-9 . Furthermore, the unique spin-valley optical selection rules 10-12 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 moiré superlattices beyond graphene.

Transport across twist angle domains in moiré graphene

“…Thus exploring the role of DWs in such systems could also be interesting. Given the recent developments in moiré materials made of multilayer graphitic systems [84,85], or transition metal dichalcogenide bilayers [7,86,87], it would be worthwhile to understand the effect of twist angle or strain domains on the electronic and excitonic physics of these materials as well.…”

“…are among the most innate tuning parameters which can fundamentally transform, thereby help us understand, many condensed matter systems. As a result of the discovery of correlated insulation [1] and superconductivity [2] in twisted bilayer graphene (TBG), a twist angle has been envisaged as a conspicuously novel control parameter that can allow various layered van der Waals materials to host myriads of intriguing phases [3][4][5][6][7].…”

Exciton g-factors in monolayer and bilayer WSe2 from experiment and theory

“…By virtue of sizable light-matter coupling governed by excitons 1 , they exhibit versatile potential for applications in photonics and optoelectronics 2,3 , opto-valleytronics 4,5 , and polaritonics 6 . Most recently, the optical interface to TMDs has been instrumental for the observation of strongly correlated electron phenomena in twisted homobilayer and heterobilayer moiré systems [7][8][9] .…”

Wigner crystals in two-dimensional transition-metal dichalcogenides: Spin physics and readout

“…As recently pointed out, monolayer transition-metal dichalcogenides (TMDs) [14] and TMD-based moiré superlattices [15][16][17] are unique platforms for realizing strongly correlated systems and the study of WCs in particular owing to the combination of reduced screening in two dimensions and a relatively high effective electron mass. Their optical bandgap offers exciting possibilities to probe quasiparticle excitations, e.g., excitons or trions [18][19][20][21] optically [22][23][24].…”