Giant Circular Dichroism Driven by Particle–Hole Symmetry Breaking in MnBi2Te4

by Prof. Xiang Yuan (East China Normal University)

Wednesday 9 Sept 2026, 10:30 → 11:30 Asia/Shanghai

Tsung-Dao Lee Institute/N4F-N400 - meeting room (Tsung-Dao Lee Institute)

Host: Prof. Nanlin Wang

Venue: TDLI Meeting Room N400

Tencent Meeting link:  https://meeting.tencent.com/dm/S9Zepa8bxdZz

Meeting ID: 692449779, no password

 

Abstract:

Circular dichroism, arising from the differential interaction of circular polarized photon between chiral light and matter, plays an important role in applications such as molecular sensing and optical communications. However, the intrinsic circular dichroic responses in most materials are typically weak and limited to narrow spectral ranges, especially in the infrared regime.

In this talk, I will introduce an intrinsic giant circular dichroism induced by particle-hole asymmetry in the type-II Weyl semimetal Mn(Bi1-xSbx)2Te4. By employing high-field infrared spectroscopy, we observe sharp Landau-level optical transitions emerging in the ferromagnetic phase. These transitions originate from the intrinsic band-nesting effect associated with the type-II Weyl electronic structure. A k·p model reveals that the particle-hole symmetry breaking in MnBi₂Te₄ arises from ferromagnetism-induced asymmetric spin-orbit coupling. The substantial difference between the Fermi velocities of the conduction and valence bands reconstructs the wavefunction characteristics of Landau levels, resulting in optical transitions that strongly couple to one circular polarization while being nearly forbidden for the opposite polarization. Polarization-resolved magneto-infrared spectroscopy experimentally confirms this pronounced circular polarization selectivity and further reveals its broadband response.

Our work demonstrates that particle-hole symmetry breaking provides an effective route toward realizing polarization-selective optical functionalities in quantum materials. I will also introduce recent developments of high-field infrared spectroscopy instrumentation.

 

Biography:

Xiang Yuan received his B.S. and Ph.D. degrees in Physics from Fudan University in 2014 and 2019, respectively. He joined the State Key Laboratory of Precision Spectroscopy at East China Normal University in 2019.

His research focuses on experimental studies of topological quantum materials under magnetic fields, with an emphasis on the development of advanced high-field infrared spectroscopy techniques. His major achievements include the discovery of one-dimensional Weyl fermions, three-dimensional van Hove singularities, and giant circular dichroism effects in quantum materials.

He has published representative works as the first or corresponding author in Nature and 3 Nature Materials. He has been recognized as the MIT Technology Review Innovators Under 35, received the Junhao Youth Scientist Award.