Bilayer Wigner crystals in a transition metal dichalcogenide heterostructure

Abstract

A Wigner crystal, a regular electron lattice arising from strong correlation effects 1-6 , is one of the earliest predicted collective electronic states. This many-body state exhibits quantum and classical phase transitions 7 and has been proposed as a basis for quantum information processing applications 8, 9 . In semiconductor platforms, two-dimensional Wigner crystals have been observed under magnetic field 10-17 or moiré-based lattice potential 18-21 where the electron kinetic energy is strongly suppressed. Here, we report bilayer Wigner crystal formation without a magnetic or confinement field in atomically thin MoSe2 bilayers separated by hexagonal boron nitride. We observe optical signatures of robust correlated insulating states formed at symmetric (1:1) and asymmetric (4:1 and 7:1) electron doping of the two MoSe2 layers at cryogenic temperatures. We attribute these features to the bilayer Wigner crystals formed from two commensurate triangular electron lattices in each layer, stabilized via inter-layer interaction 22, 23 . These bilayer Wigner crystal phases are remarkably stable and undergo quantum and thermal melting transitions above a critical electron density of up to 6 ´ 10 12 cm -2 and at temperatures of ~40 K. Our results demonstrate that atomically thin semiconductors provide a promising new platform for realizing strongly correlated electronic states, probing their electronic and magnetic phase transitions, and developing novel applications in quantum electronics and optoelectronics 24-28 .Atomically thin heterostructures made of graphene and transition metal dichalcogenide (TMD) monolayers can host a variety of correlated electronic states [29][30][31][32][33] . Recent advances in materials growth and heterostructure fabrication have enabled the preparation of high-quality heterostructures with minimal disorder [34][35][36][37][38] . The large effective masses of charge carriers 39, 40 and the weak Coulomb screening in TMDs suppress the Fermi energy and enhance electron

Dynamical mean field theory of moiré bilayer transition metal dichalcogenides: phase diagram, resistivity, and quantum criticality

“…Longer ranged hopping and interaction terms, neglected in Eq. 1, are believed not to be of qualitative importance for the carrier concentrations of main interest here, which are near one electron per moiré unit cell, although they may be relevant for Wigner crystal states reported at much lower carrier concentrations [40,41].…”

Melting of generalized Wigner crystals in transition metal dichalcogenide heterobilayer Moiré systems

“…In particular, we presented a microscopic mechanism for the formation of the nematic-II state via π/3 intersections between columnar fragments. As a subject of future work, it would be interesting to study the implications of our findings for the melting of WCs without a lattice potential, such as those recently observed in [24,25].…”

Optical signatures of periodic magnetization: the moiré Zeeman effect

“…Umklapp signatures of a ferromagnetic triangular lattice.-Recent experiments have demonstrated the possibility to generate periodic charge distributions at low car-rier density such as Wigner crystals in TMD monolayers [22,25] and Mott-Wigner states in twisted bilayers [10,26,27]. The emergence of excitonic Umklapp resonances in optical spectroscopy due to exciton-electron interactions has served as a direct probe of broken translational invariance of electrons [10,22].…”