Sun Dong's research group and collaborators in the School of Physics used the mid-infrared circularly polarized photoelectric effect to provide strong evidence for Weyl Semiconductor

Professor Sun Dong, Center for Quantum Materials Science, School of Physics, School of Physics, Peking University, and Professor Zeng Changgan, Hefei National Research Center for Microscale Material Science, School of Physics, and Key Laboratory of Strongly Coupled Quantum Materials Physics, Chinese Academy of Sciences, cooperated with Professor Zeng Changgan of Hefei National Research Center for Microscale Material Science, University of Science and Technology of China to measure tellurium (Te) as a circular polarization correlation photocurrent at mid-infrared wavelength, which provided strong optical evidence
to support tellurium (Te) as a "Weil semiconductor" 。 The research results, entitled "Unveiling Weyl-related optical responses in semiconducting tellurium by mid-infrared circular photogalvanic effect", were published online on September 16, 2022 in Nature Communications
.

Due to its non-banal band structure, Weyl semimetals have produced many novel topological properties related to them, which have attracted a wide range of research interest
in recent years.
Previously, the topological properties associated with the Weyl cone were often regarded as the unique properties of semi-metallic materials, and if a series of favorable properties such as flexible controllability of semiconductors can be combined with the novel properties of Weyl semi-metals to realize "Weyl semiconductors", there will be great application potential
in high-performance electronic devices and optoelectronic devices in the future.
Therefore, after revealing various topological properties of Weyl semimetals, "Weyl semiconductors" is one of
the next important research contents in this field.

Tellure (Te) has traditionally been considered a narrow bandgap semiconductor, and recently, transport measurements have reported potential evidence of the presence of Weyl points in Te, making Te a possible system for the realization of "Weyl semiconductors", but more evidence is still needed experimentally to help confirm its "Weyl semiconductor" properties
.
The chirality of the Weyl cone is one of the characteristics of the Weyl semimetal, which leads to the formation of a spin-flipped band structure near the Weyl point, and the associated circularly polarized optical selection law
.
The sign inversion of the circularly polarized photoelectric effect (CPGE) at wavelengths of 4.
0 and 10.
6 microns was observed in the experiment, which indicates that different optical transition processes correspond to two wavelengths: one transition occurs inside the Weyl cone, and the chirality of the Weyl point brings about the spin flip between the adjacent two bands, while the other occurs between
two different Weyl cones spanning the band gap.
This experimental phenomenon is consistent
with the calculated results of the transition matrix elements.
This experimental phenomenon reveals the unique optical selection rules that Te follows during transitions within a single Weyl cone and between different Weyl cones, providing strong optical evidence
to support Te as a "Weyl semiconductor".
With ultra-high mobility, adjustable strain and thickness bandgaps, two-dimensional layered structure and excellent air stability, Veil Semiconductor Te not only provides an ideal platform for exploring and regulating the physics of singular topologies in semiconductor materials, but also provides unprecedented application prospects
for the realization of multifunctional Weyl devices.

Figure A: Schematic diagram of circularly polarized optical selection rules for transitions near different chiral Weyl points; Figure b: The energy band position corresponding to photon transitions of different wavelengths in Te; Fig.
C and d: Circular polarization-dependent photocurrent measurements at 4μm and 10.
6μm wavelengths, respectively, with opposite CPGE symbols at 4μm and 10.
6μm

Ma Junchao, a 2017 graduate student at the Center for Quantum Materials Science, School of Physics, Peking University, is the first author of the paper, Sun Dong and Zeng Changgan are co-corresponding authors, and other major collaborators include Professor Wang Zhengfei of the National Research Center for Microscale Material Science of the University of Science and Technology of China, and researcher Cheng Jinluo of
the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences.
The research work has been supported
by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Beijing Natural Science Foundation.