Observation of coupled states in monolayer WS2 double quantum wells

Abstract

Transition metal dichalcogenides have attracted enormous attention in valleytronics due to the valley-contrasting properties originated from the broken inversion symmetry and time-reversal symmetry. However, although many studies have been conducted until recently, challenges still exist for practical application owing to the limitation of the valley lifetime, depolarization lifetime caused by intervalley scattering, electron-hole coulomb exchange interaction, etc. Recently, the rapid progress in the study to suppress these effects has been made in the various systems such as heterostructure, bilayer system to reduce the spatial overlap of wavefunction. In this work, we suggest the coupled double quantum well struc-tures based on monolayer WS2 separated by hexagonal boron nitride barrier layers. From photoluminescence measurements, we observed coupled states not seen at single quantum well, which have the dependence on the twist angle between upper quantum well and lower quantum well. This can be understood by the formation of coupled states with antisymmet-ric and symmetric of wavefunctions confined in coupled double quantum wells.