image: (a), Optical image of 12-electrode device with active areas protected by h-BN; (b) the relationship between the first-order transverse Hall voltage and longitudinal voltage at 100 K and (c) the relationship between the second-order & third-order transverse nonlinear Hall voltage and longitudinal voltage at 100 K; (d) The relationship between the third-order transverse nonlinear Hall voltage and the longitudinal voltage measured at room temperature. All measured voltage signals in the transverse direction are perpendicular to the current direction, which is marked in (a). view more
Credit: ©Science China Press
The Hall effect is a mainstream direction in the study of condensed matter physics. Recently, the second-order Hall effect that does not require a magnetic field has recently been discovered in non-magnetic systems, expanding a new member of the Hall effect family. The second-order nonlinear Hall effect is deeply related to symmetry and topology, and one of its important physical mechanisms is attributed to the Berry curvature dipole. When linear and second-order Hall effects are suppressed by the symmetry of the system, searching for higher order nonlinear Hall effects has become a hot topic.
Recently, a jointed research group headed by Professor Weibo Gao from Nanyang Technological University and Professor Shengyuan Yang from Singapore University of Science and Design has made a series of progress in the third-order nonlinear Hall effect. They observed the third-order nonlinear Hall effect in MoTe2 and WTe2 materials in 2021 [Nat. Nanotechnol. 16, 869–873 (2021)]. By the theoretical analysis, they pointed out that the third-order effect originates from Berry-connection polarizability, rather than the Berry curvature dipole which plays an important role in the second-order nonlinear Hall effect . It is a completely new physical mechanism that causes the nonlinear Hall [see their recent research papers: Phys. Rev. B 105, 045118 (2022)].
However, the third-order nonlinear Hall effect in MoTe2 and WTe2 can only exist at low temperatures (<100K), which hinders its potential application. Therefore, whether the third-order nonlinear Hall effect can be observed at room temperature has become a key problem that needs to be solved urgently. Recently, the National Science Review (NSR) magazine published an online research work by this research group. The research team observed a significant room temperature third-order nonlinear Hall effect in type-II Weyl semimetal TaIrTe4, and the effect can be stable for several months at room temperature. The room-temperature characteristics and high stability of the third-order nonlinear Hall of TaIrTe4 make it a good research platform for studying the third-order nonlinear Hall effect.
They also explored the physical mechanisms of the presence of the third-order nonlinear Hall effect at room temperature in TaIrTe4. By comparing with the third-order nonlinear effect of MoTe2, they found that the contribution of Berry-connection polarizability in TaIrTe4 is greater than that in MoTe2. Moreover, the third-order nonlinear conductance contributed by the Berry-connection polarizability decays much slower with temperature than that contributed by extrinsic Drude scattering. This may be the reason why the third-order nonlinear Hall effect can be observed at room temperature in TaIrTe4. This finding demonstrates the possibility of nonlinear Hall effects at room temperature and deepens the understanding of the effect of Berry-connection polarizability on the third-order Hall effect. This work discovers the third-order nonlinear Hall effect at room temperature for the first time, which will further promote possible room temperature applications of the effect in Weyl semimetals.
This study was led by Prof. Wei-bo Gao (Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University), Prof. Shengyuan A. Yang (Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University). The young Scientist Dr. Cong Wang (College of Mathematics and Physics, Beijing University of Chemical Technology) and Dr. Ruichun Xiao (Institute of Physical Science and Information Technology and Information Materials, Anhui University), were the co-first authors of the article, respectively, and Dr. Huiying Liu (Singapore University of Science and Design) participated in the construction of theoretical models. The project was funded by the Natural Science Foundation of Singapore, the Ministry of Education of Singapore, the National Natural Science Foundation of China, and the Fundamental Research Funds for the Central Universities.
See the article:
Room temperature third-order nonlinear Hall effect in Weyl semimetal TaIrTe4
https://doi.org/10.1093/nsr/nwac020
Journal
National Science Review