A PhD student Chui-Zhen Chen and his advisor Prof. X.C. Xie of The International Center for Quantum Materials (ICQM), School of Physics, Peking University, published an article in “Physics Review Letter” with the title: Disorder and Metal-Insulator Transitions in Weyl Semimetals (PRL. 115, 246603). This work was done in collaboration with Pro.Juntao Song from Hebei Normal University, Prof. Hua Jiang from Soochow University, Prof. Qing-feng Sun from ICQM, and Pro. Ziqiang Wang from Boston College.

The newly proposed Weyl semimetal (WSM), a time-reversal symmetry breaking topological quantum state of matter, has been observed recently in real materials (TaAs and NbAs) as well as on optical lattices. It is thus timely to study the effects of disorder, localization, and Anderson type of metal-insulator transitions in WSM systems, both for their direct experimental relevance and for their fundamental value in advancing the understanding of the interplay between randomness and topological order.

C.-Z. Chen et al. do so in this work using both numerical and analytical approaches. Because the WSM has novel gapless excitations, i.e. the Weyl nodes in the bulk and Fermi arcs on the surface, they find an unexpectedly rich phase diagram in the presence of disorder [see Fig.(b)] that is highlighted by the WSM to quantum anomalous Hall insulator transition; the WSM to 3D anomalous Hall metal transition; and the normal band insulator to WSM transition. They address the important issue on the stability of the Weyl nodes and Fermi arcs against weak disorder and obtain the complete phase behaviors for all disorder strengths by calculating the localization length and the Hall conductivity. They propose that the novel disorder-induced phase transitions can be realized on photonic lattices.

The work was supported by National Basic Research Programs of China, National Natural Science Foundation of China, and Collaborative Innovation Center of Quantum Matter, China.