Mayes Morgan, Farahmand Farima, Grossnickle Maxwell, Lohmann Mark, Aldosary Mohammed, Li Junxue, Aji Vivek, Shi Jing, Song Justin C W, Gabor Nathaniel M
Department of Physics and Astronomy, University of California, Riverside, CA 92521.
Laboratory of Quantum Materials Optoelectronics, University of California, Riverside, CA 92521.
Proc Natl Acad Sci U S A. 2023 Sep 26;120(39):e2221815120. doi: 10.1073/pnas.2221815120. Epub 2023 Sep 18.
Photocurrent in quantum materials is often collected at global contacts far away from the initial photoexcitation. This collection process is highly nonlocal. It involves an intricate spatial pattern of photocurrent flow (streamlines) away from its primary photoexcitation that depends sensitively on the configuration of current collecting contacts as well as the spatial nonuniformity and tensor structure of conductivity. Direct imaging to track photocurrent streamlines is challenging. Here, we demonstrate a microscopy method to image photocurrent streamlines through ultrathin heterostructure devices comprising platinum on yttrium iron garnet (YIG). We accomplish this by combining scanning photovoltage microscopy with a uniform rotating magnetic field. Here, local photocurrent is generated through a photo-Nernst type effect with its direction controlled by the external magnetic field. This enables the mapping of photocurrent streamlines in a variety of geometries that include conventional Hall bar-type devices, but also unconventional wing-shaped devices called electrofoils. In these, we find that photocurrent streamlines display contortion, compression, and expansion behavior depending on the shape and angle of attack of the electrofoil devices, much in the same way as tracers in a wind tunnel map the flow of air around an aerodynamic airfoil. This affords a powerful tool to visualize and characterize charge flow in optoelectronic devices.
量子材料中的光电流通常在远离初始光激发的全局接触处收集。这种收集过程具有高度的非局域性。它涉及到光电流流动（流线）的复杂空间模式，该模式远离其主要光激发，并且敏感地依赖于集流接触的配置以及电导率的空间不均匀性和张量结构。直接成像以追踪光电流流线具有挑战性。在这里，我们展示了一种显微镜方法，通过包含钇铁石榴石（YIG）上的铂的超薄异质结构器件来成像光电流流线。我们通过将扫描光电压显微镜与均匀旋转磁场相结合来实现这一点。在这里，局部光电流通过光能斯特型效应产生，其方向由外部磁场控制。这使得能够在各种几何形状中绘制光电流流线，这些几何形状包括传统的霍尔条形器件，以及称为电箔的非常规翼形器件。在这些器件中，我们发现光电流流线根据电箔器件的形状和攻角显示出扭曲、压缩和扩展行为，这与风洞中示踪剂描绘空气动力学翼型周围气流的方式非常相似。这提供了一个强大的工具来可视化和表征光电器件中的电荷流动。
