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Ultrafast dynamics in van der Waals heterostructures


Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two-dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer-to-layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited-state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long-lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.

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E.Y.M. acknowledges support from the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE-AC02-76SF00515. T.F.H. acknowledges support from the AMOS programme, Chemical Sciences, Geosciences, and Biosciences Division, Basic Energy Sciences, US Department of Energy under contract DE-AC02-76-SF00515 and from the Betty and Gordon Moore Foundation’s EPiQS Initiative through grant no. GBMF4545. O.K. acknowledges the support of the Rothschild Fellowship of Yad Hanadiv Fund, Israel, the Viterbi Fellowship of the Andrew and Erna Viterbi Department of Electrical Engineering, Technion, Israel, and the Betty and Gordon Moore Foundation’s EPiQS Initiative through grant no. GBMF4545. F.W. and E.C.R. acknowledge support from the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the US Department of Energy under contract no. DE-AC02-05-CH11231 (van der Waals heterostructures programme, KCWF16). C.J. acknowledges support from the National Science Foundation EFRI programme (EFMA-1542741). E.C.R acknowledges support from the Department of Defense through the National Defense Science & Engineering Graduate (NDSEG) Fellowship programme.

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Correspondence to Feng Wang or Tony F. Heinz.

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Further reading

Fig. 1: Band alignment in vertical vdW heterostructures of TMDCs.
Fig. 2: Experimental studies of ultrafast charge transfer in vertical TMDC heterostructures.
Fig. 3: Theoretical concepts explaining the robust and ultrafast nature of charge transfer in TMDC heterostructures52.
Fig. 4: Dynamics of spin–valley information carriers in TMDC materials.
Fig. 5: Potential origin of intervalley scattering in WSe2/MoS2 heterostructures.
Fig. 6: Spin–valley transport in a vdW heterostructure.