Fig. 1: WS2/WSe2 bilayer as a platform for correlated physics.
From: Excitonic Mott insulator in a Bose-Fermi-Hubbard system of moiré WS2/WSe2 heterobilayer
a Schematic of the WS2/WSe2 dual-gate device. The TMD heterobilayer is embedded between two symmetric gates: top gate (TG) and bottom gate (BG). b Depiction of the type-II band alignment of the bilayer. The blue and red curves denote bands from WS2 and WSe2, respectively. The shaded ellipse indicates the formation of interlayer excitons composed of an electron from the WS2 conduction band and a hole from the WSe2 valence band. c Phase diagram of the system. The population of the moiré lattice can be controlled via two independent parameters: the gate voltage changes the electronic filling factor (νe), and the optical pump creates a population of excitons, proportional to the input intensity. In the gray area, the system behaves as a mixed gas of bosonic and fermionic particles. As one approaches the upper limit (black line), the system becomes incompressible due to the saturation of single-occupancy states. d–f Interlayer exciton formation under optical excitation for three different regimes governed by the pump intensity (I) and νe: c low I and νe ~ 0, d low I and νe ~ 1, e high I and 0 < νe < 1. X1 (X2) denotes PL emission from singly (doubly) occupied moiré lattice sites. X2 can originate from either electron-exciton (Uex-e) or exciton–exciton (Uex-ex) double occupancies.
