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Van der Waals heterostructures made of graphene and transition metal dichalcogenides (TMD) are an emerging platform for opto-electronic, -spintronic and -valleytronic devices that could benefit from (i) strong light-matter interactions and spin-valley locking in TMDs and (ii) exceptional electron and spin transport in graphene. The operation of such devices requires significant valley polarization and valley coherence, ideally up to room temperature. Here, using a comprehensive Mueller polarimetry analysis, we report artifact-free room temperature degrees of valley polarization up to \\(40~\\%\\) and, remarkably, of valley coherence up to \\(20~\\%\\) in monolayer tungsten disulfide (WS\\(_2\\))/graphene heterostructures. Valley contrasts have been particularly elusive in molybdenum diselenide (MoSe\\(_2\\)), even at cryogenic temperatures. Upon interfacing monolayer MoSe\\(_2\\) with graphene, the room temperature degrees of valley polarization and coherence are as high as \\(14~\\%\\) and \\(20~\\%\\), respectively. Our results are discussed in light of recent reports of highly efficient interlayer coupling and exciton transfer in TMD/graphene heterostructures and hold promise for room temperature chiral light-matter interactions and coherent opto-valleytronic devices.

Non-volatile memory devices have been limited to flash architectures that are complex devices. Here, we present a unique photomemory effect in MoS\\(_2\\) transistors. The photomemory is based on a photodoping effect - a controlled way of manipulating the density of free charges in monolayer MoS\\(_2\\) using a combination of laser exposure and gate voltage application. The photodoping promotes changes on the conductance of MoS\\(_2\\) leading to photomemory states with high memory on/off ratio. Such memory states are non-volatile with an expectation of retaining up to 50 % of the information for tens of years. Furthermore, we show that the photodoping is gate-tunable, enabling control of the recorded memory states. Finally, we propose a model to explain the photodoping, and we provide experimental evidence supporting such a phenomenon. In summary, our work includes the MoS\\(_2\\) phototransistors in the non-volatile memory devices and expands the possibilities of memory application beyond conventional memory architectures.