Abstract
Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. For either application, a long valley polarization lifetime is crucial. Previous results showed that it is around picosecond in monolayer excitons, nanosecond for local excitons and tens of nanosecond for interlayer excitons. Here we show that the dark excitons in two-dimensional heterostructures provide a microsecond valley polarization memory thanks to the magnetic field induced suppression of valley mixing. The lifetime of the dark excitons shows magnetic field and temperature dependence. The long lifetime and valley polarization lifetime of the dark exciton in two-dimensional heterostructures make them promising for long-distance exciton transport and macroscopic quantum state generations.
Highlights
Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation
With magnetic field suppressed valley mixing, they serve as a microsecond valley polarization memory for indirect excitons
Electrons tend to go to the conduction band of MoSe2 and holes are confined in the valence band of WSe2, forming the indirect excitons (Fig. 1a)
Summary
Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. We show that the dark excitons in two-dimensional heterostructures provide a microsecond valley polarization memory thanks to the magnetic field induced suppression of valley mixing. The long lifetime and valley polarization lifetime of the dark exciton in two-dimensional heterostructures make them promising for long-distance exciton transport and macroscopic quantum state generations. Longer survival of excitons means longer distance of exciton transport, which is useful for excitonic devices[13,14] In another perspective, similar to monolayer TMDs, the properly aligned two-dimensional (2D) heterostructure has indirect exciton with valley degree of freedom. Experimental evidence shows the existence of dark excitons, lying tens of millielectronvolts below the bright exciton in WSe233 Their decay time is measured to be nanoseconds in monolayer TMD34. This is two orders longer than the case without an applied magnetic field
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