Photocurrent as a multiphysics diagnostic of quantum materials

The photoexcitation life cycle from incident photon (and creation of photoexcited electron–hole pair) to ultimate extraction of electrical current is a complex multiphysics process spanning across a range of spatiotemporal scales of quantum materials. Photocurrent is sensitive to a myriad of physical processes across these spatiotemporal scales, and over the past decade it has emerged as a versatile probe of electronic states, Bloch band quantum geometry, quantum kinetic processes and device characteristics of quantum materials. This Technical Review outlines the key multiphysics principles of photocurrent diagnostics, for resolving band structure and characterizing topological materials, for disentangling distinct types of carrier scattering that can range from femtosecond to nanosecond timescales and for enabling new types of remote-sensing protocols and photocurrent nanoscopy. These distinctive capabilities underscore photocurrent diagnostics as a novel multiphysics probe for a growing class of quantum materials with properties governed by physics spanning multiple spatiotemporal scales. Ministry of Education (MOE) Q.M. was supported through NSF Career DMR-2143426 and the CIFAR Azrieli Global Scholars programme. R.K.K. acknowledges the EU Horizon 2020 programme under the MarieSkłodowska-Curie grant numbers 754510 and 893030. S.-Y.X. was supported through NSF Career (Harvard fund 129522) DMR-2143177. F.H.L.K. acknowledges support from the ERC TOPONANOP (726001), the Government of Spain (PID2019-106875GB-I00; Severo Ochoa CEX2019-000910-S (MCIN/AEI/10.13039/501100011033)), Fundació Cellex, Fundació Mir-Puig and Generalitat de Catalunya (CERCA, AGAUR, SGR 1656). Furthermore, the research leading to these results has received funding from the European Union’s Horizon 2020 under grant agreement numbers 881603 (Graphene flagship Core3) and 820378 (Quantum flagship). J.C.W.S. acknowledges support from the Singapore MOE Academic Research Fund Tier 3 Grant number MOE2018-T3-1-002.