Prof. Zhiqiang Mao [Tulane University, USA]

Title: Relativistic Fermions Generated by Square Lattices in Layered Compounds

Time: 2:00 - 3:00 PM, Monday, May 15, 2017

Place: Conference room C206, HPSTAR (Beijing)

Host: Dr. Hong Xiao

Abstract

Recent discoveries of three dimensional (3D) topological semimetals, including Dirac semimetals (DSM), Dirac nodal-line semimetals and Weyl semimetals, have generated immense interests since they represent new topological states of quantum matters. Both Dirac and Weyl semimetals feature relativistic fermions with linearly dispersing excitations. In this talk, I will first give a brief introduction to this emerging area and discuss how to characterize the properties of Dirac/Weyl fermions. Then I will present our recent studies on topological semimetals [1-6].  I will show nearly massless Dirac fermions generated by 2D Sb layers coexists with ferromagnetism in Sr1-yMn1-zSb2, which offers a rare opportunity to investigate the effect of time reversal symmetry breaking on the electronic band structure and explore a possible ferromagnetic Weyl state [1-2]. I will also report our recent discovery of two new nodal line semimetals – ZrSiSe and ZrSiTe [4]. The nodal-line semimetals exhibit Dirac cones along a one dimensional line/loop in their electronic structure, contrasted with the Dirac/Weyl cones with discrete nodes in Dirac/Weyl semimetals. We have found signatures of nodal-line fermions from quantum oscillation experiments in these two materials and demonstrated that their atomically thin crystals are accessible via mechanical exfoliation, which raises the possibility of realizing the theoretically predicted 2D topological insulators [7] in monolayers of ZrSiSe and ZrSiTe. Finally I will discuss exotic quantum transport behavior of Weyl semimetal YbMnBi2 [6], which results from the zeroth Landau Level, a unique property of topological materials.

  References:

   [1] J. Hu et al., Scientific Report 6, 18674 (2016)

   [2] J.Y. Liu et al., arXiv:1507.07978.

   [3] J.Y. Liu et al., Scientific Report 6, 30525 (2016).

   [4] J. Hu et al., PRL 117, 016602 (2016).

   [5] J. Hu et al., arXiv: 1604.01567

   [6] J. Hu et al., arXiv: 1608.05956

   [7] Q. Xu et al., PRB 92, 205310 (2015).

Biography of the Speaker:

Prof. Zhiqiang Mao obtained his PhD from University of Science and Technology of China (USTC) in 1992. He worked as postdoctoral scholar in Kyoto University during 1997 to 2000 and in Department of Physics, Pennsylvania State University during 2000 to 2002. He worked in Department of Physics and Engineering Physics, Tulane University as assistant professor since 2002. He is promoted to associated professor in 2007 and full professor in 2009. He was Elected fellow of the American Physical Society in 2015. The Mao group’s research at Tulane aims to discover and synthesize novel quantum materials with emergent phenomena and investigate their underlying physics. His current research is focused on four sub-directions: a) emergent quantum phenomena in strongly correlated oxides; b) interplay between magnetism and superconductivity in iron-based superconductors; c) novel functional two-dimensional (2D) materials of ternary transition metal chalcogenides; d) topological Dirac and Weyl semimetals. Total publications: 254. The total citation count exceeds 6150 with H-index = 39 (from Web of Science); 26 in PRLs, 4 in Nature, 1 in Nature Materials, 1 in Nature Physics, 2 in Nature Communications, 1 in Science, 4 in Scientific Report, 70 in PRB)