Title

Linear and second order responses in topological semimetals

Speaker

Dr. Yan Sun

Max Planck Institute for Chemical Physics of Solids, Germany               

Time

10：00am, January 16, 2019

Place

Room 9004 at the HFNL building

Dr. Yan Sun is a research group leader in Max Planck Institute for Chemical Physics of Solids. He received his Ph.D degree from Shenyang National Laboratory for Material Science, Institute of Metal Research, Chinese Academy of Sciences in 2014, with supervisors Prof. Xing-Qiu Chen, and Prof. Yiyi Li. After graduation, he started his post-doctor study in Max Planck Institute for Chemical Physics of Solids with Dr. Binghai and Prof. Claudia Felser. In 2017, he became a research group leader responsible for the theoretical study of topological systems. His research interest mainly focuses on the understanding the physical properties, including transport and surface states, of materials based on the electronic structure and linear response theory. So far, he has published more than 40 research papers, and gets more than 2800 citations.

Abstract

We have found that the strong spin Hall effect in TaAs is mainly dominated from the Weyl points and nodal-line-like Fermi surface, which implies a strong interplay between the topological band structure and Berry curvature in topological semimetals. With this guiding principle, we have successfully understood the strong spin Hall effect in IrO₂ and found the nodal line band structures in it. This principle was further verified by our developed database. Generalizing this principle to time reversal symmetry broken system, we have proposed strong anomalous Hall effect in magnetic Weyl semimetal Co₃Sn₂S₂.Owing to the low charge carrier density and large Berry curvature from the nodal line band structure, the anomalous Hall conductivity and anomalous Hall angle experimentally reach up to 1130 S/cm and 20%, respectively. Further, the anomalous Hall effect can even exist with zero net moment in the absence of the symmetry operation that changes the sign of Berry curvature, and the anomalous Hall effect can be strongly enhanced by the special band structures of Weyl points and nodal lines. Following this guiding direction, we have predicted a strong anomalous Hall effect in the compensated ferrimagnetic Weyl semimetal Ti₂MnAl and noncollinear antiferromagnetic Weyl metal Mn₃Ge with vanishing net magnetic moments. Owing to time reversal symmetry, anomalous Hall effect is forbidden in the first order perturbation, but the higher order response can exist. We have studied the Berry curvature dipole induced non-linear anomalous Hall effect, which was experimentally observed very recently.