  Analogous to conventional charge-based electronics, valleytronics aims at
encoding data via the valley degree of freedom, enabling new routes for
information processing. Long-lived interlayer excitons (IXs) in van der Waals
heterostructures (HSs) stacked by transition metal dichalcogenides (TMDs) carry
valley-polarized information and thus could find promising applications in
valleytronic devices. Although great progress of studies on valleytronic
devices has been achieved, nonvolatile valleytronic memory, an indispensable
device in valleytronics, is still lacking up to date. Here, we demonstrate an
IX-based nonvolatile valleytronic memory in a WS2/WSe2 HS. In this device, the
emission characteristics of IXs exhibit a large excitonic/valleytronic
hysteresis upon cyclic-voltage sweeping, which is ascribed to the
chemical-doping of O2/H2O redox couple trapped between the TMDs and substrate.
Taking advantage of the large hysteresis, the first nonvolatile valleytronic
memory has been successfully made, which shows a good performance with
retention time exceeding 60 minutes. These findings open up an avenue for
nonvolatile valleytronic memory and could stimulate more investigations on
valleytronic devices.
