Valley polarization of moir\'e interlayer exciton complexes driven by many-body interactions

Abstract

Localized interlayer excitons (IX) in moir\'e transition metal dichalcogenide heterostructures can both probe and participate in many-body states hosted by the moir\'e superlattice. When the IX density is small compared to the moir\'e lattice density, the formation of incompressible charge crystals at fractional electronic moir\'e fillings modifies exciton-charge scattering, leading to enhanced lifetimes in photoluminescence (PL) measurements. At high IX densities, the exciton dynamics are altered by the emergence of an excitonic Mott insulator and the formation of doubly-occupied sites (IXX). Here, we investigate the IX PL lifetime and valley polarization in an R-type $\mathrm{WSe_2}$/$\mathrm{WS_2}$ bilayer across a wide range of IX and charge densities. While previous studies reported a decrease of polarization in time-integrated measurements in charge-incompressible phases, our results show that this arises not from enhanced intervalley scattering, but from a dilution of the valley polarization by the dramatic enhancement of IX lifetimes. At high excitation densities, we probe the dynamics of the IXX and show that despite the nominal antiparallel valley configuration of the two constituent excitons, a strong, anomalous valley polarization develops as the IXX population decays. Our results shed light on the complex exciton and valley dynamics of IX and demonstrate that they are strongly modified by the rich many-body physics of moir\'e heterobilayers.