Quantum sensors can be used to reveal a surprising new mechanism for converting light into electricity in Weyl semimetals, 电子游戏软件 Assistant Professor of 物理 布莱恩周 and colleagues report in the journal 自然物理.
许多现代技术, 比如照相机, 光纤网络, and solar cells rely on the conversion of light into electrical signals. 但是对于大多数材料, shining a light onto their surface will not generate any electricity because there is no preferred direction for the electricity to flow. The unique properties of electrons in Weyl semimetals have made them a focus of researchers trying to overcome those limits and develop novel optoelectronic devices.
In the above image from the Zhou Lab at 电子游戏软件, photocurrent flows in (illustrated in blue) along one crystal axis of the Weyl semimetal and flows out (illustrated in yellow/orange) along the perpendicular axis. (电子游戏软件-led team develops new quantum sensor technique to image and understand the origin of photocurrent flow in Weyl semimetals. (CC BY-NC-ND)
“Most photoelectrical devices require two different materials to create an asymmetry in space,周说, who worked with eight BC colleagues and two researchers from the Nanyang Technological University in Singapore. “在这里, we showed that the spatial asymmetry within a single material – in particular the asymmetry in its thermoelectric transport properties – can give rise to spontaneous photocurrents.”
The team studied the materials tungsten ditelluride and tantalum iridium tetratelluride, which both belong to the class of Weyl semimetals. 电子游戏正规平台ers have suspected that these materials would be good candidates for photocurrent generation because their crystal structure is inherently inversion asymmetric; that is to say, the crystal does not map onto itself by reversing directions about a point.
Zhou’s research group set out to understand why Weyl semimetals are efficient at converting light into electricity. Previous measurements could only determine the amount of electricity coming out of a device, like measuring how much water flows from a sink into a drainpipe. To better understand the origin of the photocurrents, Zhou’s team sought to visualize the flow of electricity within the device – similar to making a map of the swirling water currents in the sink.
“作为项目的一部分, 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,电子游戏正规平台生王宇轩说, 手稿的第一作者, 说.
The team found the electrical current flowed in a four-fold vortex pattern around where the light shined on the material. The team further visualized how the circulating flow pattern is modified by the edges of the material and revealed that the precise angle of the edge determines whether the total photocurrent flowing out of the device is positive, 负, 或零.
布莱恩周
“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 to say, differences in how heat is converted to current along the different in-plane directions of the Weyl semimetal,周说.
令人惊讶的是, the appearance of anisotropic thermopower is not necessarily related to the inversion asymmetry displayed by Weyl semimetals, 因此, may be present in other classes of materials.
“Our findings open a new direction for searching for other highly photoresponsive materials,周说. “It showcases the disruptive impact of quantum-enabled sensors on open questions in materials science.”
Zhou 说 future projects will use the unique photocurrent flow microscope to understand the origins of photocurrents in other exotic materials and to push the limits in detection sensitivity and spatial resolution.
In addition to Zhou and Wang, co-authors of the report “Visualization of bulk and edge photocurrent flow in anisotropic Weyl semimetals” include 电子游戏软件 Associate Professor of 物理 Ying Ran, 物理学教授David Broido, and Assistant Professor of 物理 Fazel Tafti; graduate students Xin-Yue Zhang, 托马斯·格雷厄姆, and Xiaohan Yao; and post-doctoral researcher Chunhua Li; as well as Nanyang Technological University Professor Zheng Liu and post-doctoral researcher Ruihuan Duan.
Ed Hayward | University Communications | February 2023