A Surprise New Approach to Using Light as Electricity

Brian Zhou, an Assistant Professor of Physics at Boston College, and his colleagues discovered a surprising new technique for using quantum sensors to convert light into electricity in Weyl semimetals in a recent paper that was published in the journal Nature Physics.

The conversion of light into electrical signals is the foundation upon which many modern technologies, including solar panels, fiber optic systems, and cameras, are built. However, due to the lack of a specific direction in which electricity flows, simply shining light on the surface of most materials does not generate electricity. Researchers are investigating the distinctive properties of electrons in Weyl semimetals in an effort to circumvent these limitations and develop brand-new optoelectronic devices.

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Zhou, who collaborated with eight BC colleagues and two Nanyang Technological University in Singapore, stated, “Most photoelectrical devices require two different materials to create an asymmetry in space.” In this study, we demonstrated that spontaneous photocurrents can result from a single material’s thermoelectric transport properties and spatial asymmetry.

The Weyl semimetals of tantalum iridium tetratelluride and tungsten ditelluride were the subjects of the team’s research. Because of their inherent inversion-asymmetric crystal structure, researchers have hypothesized that these materials would be suitable for the generation of photocurrents; Specifically, the crystal does not reverse directions around a point to map onto itself.

The goal of Zhou’s group of researchers was to learn why Weyl semimetals are so effective at converting light into electricity. Measurements in the past could only tell you how much electricity was coming out of a device, like how much water flows into a drainpipe from a sink. Zhou’s team wanted to visualize the flow of electricity within the device, similar to making a map of the swirling water currents in the sink, in order to better comprehend where the photocurrents came from.

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According to graduate student Yu-Xuan Wang, lead author of the manuscript, “as part of the project, we developed a new technique using quantum magnetic field sensors called nitrogen-vacancy centers in diamond to image the local magnetic field produced by the photocurrents and reconstruct the full streamlines of the photocurrent flow.”

The team discovered that the electrical current flowed in a four-fold vortex around the material where the light was shining. The team also showed how the material’s edges change the circulating flow pattern. They found that the angle of the edge determines whether the device’s total photocurrent is positive, negative, or zero.

Zhou stated, “These never-before-seen flow images allowed us to explain that the photocurrent generation mechanism is surprisingly due to an anisotropic photothermoelectric effect – that is, differences in how heat is converted to current along the different in-plane directions of the Weyl semimetal.” “These never-before-seen flow images”

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It is surprising that anisotropic thermopower does not always correspond to the inversion asymmetry of Weyl semimetals; consequently, it may be present in other types of materials.

Zhou stated, “Our findings open a new direction for the search for other materials that are highly photoresponsive.” It demonstrates the disruptive effect of quantum-enabled sensors on material science’s unanswered questions.

Zhou said future tasks will utilize the exceptional photocurrent stream magnifying lens to comprehend the starting points of photocurrents in other colorful materials and to stretch the boundaries in identification responsiveness and spatial goal.

An example: Yu-Xuan Wang, Xin-Yue Zhang, Chunhua Li, Xiaohan Yao, Ruihuan Duan, Thomas K. M. Graham, Zheng Liu, Fazel Tafti, David Broido, Ying Ran, and Brian B. Zhou published “Visualization of bulk and edge photocurrent flow in anisotropic Weyl semimetals” on January 23, 2023, in Nature Physics.
DOI: The Air Force Office of Scientific Research, the DOE/US Department of Energy, and the National Science Foundation all contributed to the study’s funding. read more….