报告人：美国普林斯顿大学 Suyang Xu博士
报告题目：Discovery of Weyl Fermion semimetal state
报告时间：周三（9月9日）上午9点半
报告地点：唐仲英楼B501
Dr. Su-Yang Xu obtained his Bs, PhD degrees from Peking University, Princeton University in 2008, 2015, respectively. Now he is a Postdoctoral Researcher in Laboratory for Topological Quantum Matter and Spectroscopy. He is interested in the fundamental physics of exotic quantum matter. He has published 12 papers in Science, Nature Phys., Nature Commun. and Phys. Rev. Lett. as the first author.
Weyl fermion materials may give rise to a new paradigm in condensed matter physics and materials science, beyond the Dirac fermions in graphene and topological insulators. They are semimetals, metals, and superconductors whose quasiparticle excitation is the Weyl fermion, a particle that is well-known in the standard model but has not been observed in vacuum. Such a fermion carries an unusual charge, the chiral charge, but, unlike other fermions, must be massless. These strange properties of the elusive particle have direct analogs in its low-energy solid-state counterpart, leading to a cornucopia of new physics and potential applications. Owing to the topological nature, the Weyl fermionic quasiparticles are robust against crystalline imperfections, and the protection does not rely on any symmetry within the framework of band theory. This gives rise to an exceptionally high mobility. Moreover, the Weyl nodes are separated in momentum space and are connected only through the crystal's boundary by a topological surface state, a Fermi arc. Such band structure would violate quantum mechanics if it arises in any purely 2D electron system. However, a Fermi arc is allowed to exist on the surface of a 3D Weyl fermion system and it may be thought of as a string that attaches a pair of magnetic monopoles. In this talk, I will present our theoretical (band structure calculation) and experimental (photoemission spectroscopy) discovery of the first Weyl semimetal in tantalum arsenide, TaAs, and its related materials. We hope that our discovery can pave the way for realizing the many predicted new physics associated with Weyl fermions.
References
1. Weyl, H. Elektron und gravitation. I. Z. Phys. 56, 330-352 (1929).
2. Balents, L. Weyl electrons kiss. Physics 4, 36 (2011).
3. Wan, X., Turner, A. M., Vishwanath, A., Savrasov, S. Y. Topological semimetal and Fermi-arc surface states in the electronic structure of pyrochlore iridates, Phys. Rev. B 83, 205101 (2011).
4. Huang, S.-M. et al. A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class. Nature Commun. 6, 7373 (2015).
5. Xu, S.-Y. et al. Discovery of a Weyl fermion semimetal and topological Fermi arcs. Science 349, 613-617 (2015).
6. Xu, S.-Y. et al. Discovery of Weyl semimetal NbAs. Nature Phys. doi:10.1038/nphys3437 (2015).
7. Xu, S.-Y. et al. Experimental discovery of Weyl semimetal TaP. Preprint at http://arxiv.org/abs/1508.03102 (2015).
8. Xu, S.-Y. et al. Observation of Fermi arc surface states in a topological metal. Science 347, 294-298 (2015).
9. Xu, S.-Y. et al. Topological Phase Transition and Texture Inversion in a Tunable Topological Insulator. Science 332, 560-564 (2011).
