Realization of the topological aspect in materials has greatly deepened our understanding on various, low-energy quasi-particles in condensed matter physics. A recent breakthrough in this field is the discovery of topological Weyl semimetals. General speaking, the Weyl quasi-particles in crystals manifest themselves as Weyl fermion, a long-sought crucial elemental particle in quantum field theory. These topologically protected Weyl quasiparticles are stable except the annihilation caused by a collision of two chirality-opposite nodes in momentum space. Such annihilation shall hardly occur when the band structure remains intact.

ICQM faculties Shuang Jia, Chi Zhang, X.C.Xie,and Prof. Junfeng Wang in Huazhong University of Science and Technology, Prof. Hai-Zhou Lu in South University of Science and Technology of China, Prof. M.Zahid Hasan in Princeton University, Prof. Neupert in University of Zurich and Prof. Hsin Lin of National University of Singapore recently conducted the high-field transport experiments on TaP, an architype Weyl semimetal. They discovered a highly unexpected sign reversal in Hall signal, which can be well explained as a signature of Weyl nodes annihilation by the catalysis of magnetic field. A very strong magnetic field can tunnel the two chirality-opposite lowest Laudau band in TaP when the reciprocal of magnetic length and momentum separation of Weyl nodes is comparable. This annihilation of the two Weyl quasiparticles leads to a sizable gap. This work can be found online in Nature Physics (2017). doi:10.1038/nphys4183.

The first author for this work is PhD student Cheng-Long Zhang in ICQM; the corresponding authors are Shuang Jia, Hai-Zhou Lu and Junfeng Wang. This work is supported by National Basic Research Program of China (Grant 80 Nos. 2013CB921901 and 2014CB239302), National Science Foundation of China and the 1000 Talents Program for Young Scientists of China.