Visualizing bulk and edge photocurrent flow in anisotropic Weyl semimetals

Abstract

Materials that rectify light into current in their bulk are desired for optoelectronic applications. In inversion-breaking Weyl semimetals, bulk photocurrents may arise due to nonlinear optical processes that are enhanced near the Weyl nodes. However, the photoresponse of these materials is commonly studied by scanning photocurrent microscopy (SPCM), which convolves the effects of photocurrent generation and collection. Here, we directly image the photocurrent flow inside the type-II Weyl semimetals WTe2 and TaIrTe4 using high-sensitivity quantum magnetometry with nitrogen-vacancy center spins. We elucidate an unknown mechanism for bulk photocurrent generation termed the anisotropic photothermoelectric effect (APTE), where unequal thermopowers along different crystal axes drive intricate circulations of photocurrent around the photoexcitation. Using simultaneous SPCM and magnetic imaging at the sample's interior and edges, we visualize how the APTE stimulates the long-range photocurrent collected in our Weyl semimetal devices through the Shockley-Ramo theorem. Our results highlight an overlooked, but widely relevant source of current flow and inspire novel photodetectors using homogeneous materials with anisotropy.

Revised submitted version; 17 pages, 4 main figures, 5 supporting figures

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• Enhanced Magnetization by Defect-Assisted Exciton Recombination in Atomically Thin CrCl${}_3$
• Intrinsic ultrafast edge photocurrent dynamics in WTe${}_2$ driven by broken crystal symmetry
• A novel device for controlling the flow of information based on Weyl fermions and some interesting remarks regarding the electromagnetic interactions of high energy particles
• Large Transverse Thermoelectric Effect in Weyl Semimetal TaIrTe${}_4$ Engineered for Photodetection
• Transverse Photoresistivity from Photothermal Current Deflection in Metal Films