Shockley-Ramo theorem and long-range photocurrent response in gapless materials

Scanning photocurrent maps of gapless materials, such as graphene, often exhibit complex patterns of hot spots positioned far from current-collecting contacts. We develop a general formalism that helps to explain the unusual features of the observed patterns, such as the directional effect and the global character of photoresponse. We show that this behavior is captured by a simple Shockley-Ramo-type framework. We examine specific examples and show that the photoresponse patterns can serve as a powerful tool to extract information about symmetry breaking, inhomogeneity, chirality, and other local characteristics of the system.