Infrared photoresponse of graphene-WTe₂ van der Waals heterojunctions

Graphene and WTe₂ are atomically thin semimetals with low density of states at their charge neutrality points. While graphene hosts Dirac-like excitations with highly symmetric electron and hole bands, WTe₂ is a type II Weyl semimetal with compensated electron-hole pockets. Here we use near-infrared scanning photocurrent microscopy to study the photoexcited electron dynamics that govern the electrical and optical conductivities at the van der Waals heterostructure interface. Interlayer photocurrent observed only at the interface between the materials, exhibits gate voltage dependence reminiscent of the photo-thermoelectric effect, previously observed in the hot carrier regime of graphene. Our measurements - which establish the essential photocurrent characteristics of this combined Dirac-Weyl system - also inform the design and development of highly sensitive infrared sensors based on van der Waals heterostructures.