Zhiqiang Mao
Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70018
Recent discoveries of three dimensional (3D) topological Dirac semimetals (DSM) in Na3Bi [1,2] and Cd3As2[3-5] and Weyl semimetals (WSM) in monopnictidesTX (T=Ta/Nb, X=As/P) [6-9] and photonic crystals[10] have generated immense interests since they represent new topological states of quantum matter. Both classes of materials feature relativistic fermions with linearly dispersing excitations. WSMs can be seen as evolving from DSMs in the presence of the breaking of time reversal symmetry (TRS) or space inversion symmetry. WSMs caused by the loss of space inversion symmetry have been experimentally realized in non-centrosymmetric crystals of TX[8-11]. In this talk, I will first give a brief introduction to this emerging area and thenpresent our recent studies on TaP and Sr1-yMn1-zSb2 (y, z < 0.1). TaP is one of the predicted WSMs. We observed two fundamental transport properties predicted for a Weyl state, i.e. the chiral anomaly-induced negative magnetoresistance and the Berry phase. Furthermore, we have generalized the Lifshitz-Kosevich (LK) formula for multiple-band Shubnikov-de Haas (SdH) oscillations and extracted the Berry phases of  for multiple Fermi pockets in TaP through the direct fits of the modified LK formula to the SdH oscillations [11]. For Sr1-yMn1-zSb2, our work showed the two-dimensional Sb layers of this material host relativistic fermions; remarkable signatures of relativistic fermions, including light effective quasiparticle mass, high carrier mobility, a  Berry phase and valley polarized interlayer conduction were all revealed from quantum transport measurements [12]. Another distinct aspect of this materials lies in its ferromagnetism. Coupling between ferromagnetism and relativistic fermion transport has also been observed. The combination of relativistic fermion behavior and ferromagnetism make this material a promising candidate for exploring the long-sought magneticWeyl semimetal.
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[8]. S.Y. Xu et al., Science 349, 613-617 (2015).
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[11] J. Hu et al, Scientific Reports 6, 18674 (2016)..
[12] J.Y. Liu et al., arXiv:1507.07978, (2015).
毛志强，美国Tulane 大学物理系教授。毛志强教授的研究组主要致力于氧化物强关联电子物理，铁基超导电性，及拓扑半金属材料的研究。在钌系氧化物研究中, 对自旋三重态超导态的建立作出过重要贡。在铁基超导电性的研究中：首先发现铁硫族超导体系的超导电性与自旋张落有关并建立该体系的相图。
毛志强教授共发表学术论文260余篇。论文被引用超过8400余次。H影响指数为43。1995年获中科院青年科学家二等奖，1996年获中国国家杰出青年基金，1997年获香港求是基金会颁发的“求是”奖，2005年获美国Research Corporation基金会Cottrell学者奖，2007年获美国自然科学基金委员会Career 奖，2015被选为美国物理学会会士。