Phonon-Fostered Valley Polarization of Interlayer Excitons in van der Waals Heterostructures

We report valley dynamics of spin-singlet (IX_S) and spin-triplet (IX_T) interlayer excitons in MoS₂/WS₂heterostructures subjected to an exchange field. Because of their interlayer character, they possess long valley coherence time in addition to long radiative lifetimes, especially for the IX_T, which is crucial for valley pseudospin manipulation. Furthermore, the exciton g-factors (g_IXS13.4 and g_IXT17.6) that are more than three times larger than that of intralayer exciton lead to giant valley Zeeman splitting (0.78-1.02 meV/T). Subjected to an exchange field, the competitive interplay among radiative relaxation, thermal excitation between IX_Sand IX_T, and phonon-assisted intervalley scattering significantly enhance photoluminescence intensity (up to 325% for IX_Sand 1075% for IX_T) in the α-valley, while suppressing it in the β-valley. Consequently, the valley polarization of IX_Sand IX_Temissions abruptly converges to unity at low temperatures. At a critical exchange field, valley-selective switching of interlayer exciton states, from IX_Tto IX_Sin the β-valley, occurs. Under such a condition, valley polarization retains very high values, above 90% for IX_Tand 85% for IX_Sat room temperature. These attractive characteristics make interlayer excitons in MoS₂/WS₂heterostructures promising for quantum applications.