Photocurrent as a multiphysics diagnostic of quantum materials

By Q. Ma, R. Krishna Kumar, Su-Yang Xu, F H L Koppens, Justin C. W. Song. Nature Reviews Physics, 2022

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Photocurrent can be used to reveal the out-of-equilibrium properties of quantum materials over a range of spatiotemporal scales. This Technical Review outlines the principles of photocurrent diagnostics and how it can be used to probe electronic states, quantum geometry and quantum kinetics of materials. The transduction of light into electrical signals (photocurrent) in quantum materials involves physical phenomena across multiple spatiotemporal scales and, therefore, photocurrent stands out as a multiphysics diagnostic tool of quantum materials. The long-range collection of locally generated photocurrent, as mediated by the streamlines of diffusion currents, enables a ‘remote’ sensing of local symmetry breaking such as p–n junctions and edges. Photocurrent spectroscopy can probe charge, spin and collective excitations with enhanced signal-to-noise characteristics and resolution for atomically thin materials with low optical weight. The intimate connection between light–matter interaction and Bloch band quantum geometry renders bulk geometric photocurrents highly sensitive to the crystal symmetry and light polarization. Technique innovation including near-field photocurrent probes as well as ultrafast photocurrents grant high spatiotemporal resolution, providing a range of new photocurrent diagnostic tools for 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.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/578fb8cc5f89cf538875e64bb9b4d1f6c0811139