We discuss some recent result on topological semi-metals. (1) The shape of the Fermi surface of topological nodal-ring semimetals at low carrier concentrations is characterized by the ring radius b/hvF. This peculiar topological property may not have a clear signature in measurable physical quantities. We demonstrate an accurate and definitive method to determine the radius of topological nodal-ring semimetals. Under a magnetic field along the ring axis, the axial magneto-optical response has a giant peak. The position of this ultrastrong response is at the frequency of exactly 2b and is independent of the strength of the magnetic field. (2) We study superconductivity states mediated by the BCS and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairings in superconducting Weyl semimetals. It is found that a mixture of BCS and FFLO pairings results in a distinctive double-gap structure for superconducting states. With a heterojunction of a Weyl semimetal and a superconducting Weyl semimetal, we demonstrate the nonholonomic Andreev reflection and show that the intra and internode Andreev reflections increase at the edges of the effective gap.
Prof. Chao ZHANG received his PhD in physics in 1987 from City University of New York, USA. From 1987 to 1989, he was a postdoctoral fellow at Max-Planck-Institute for Solid Research in Stuttgart, Germany, working on quantum magneto-transport in semiconductor nanostructures. From 1989 to 1992. He was a research associate at Canada’s Meson Research Facility in Vancouver, working on quantum coherence and dissipation in solids. Since 1993, he has been a tenured faculty member in the School of Physics, University of Wollongong, Australia. Currently he is a senior professor of physics. From 2004-2014, he served as the associate director of the Institute of Superconducting and Electronic Materials. He is a Fellow of Australian Institute of Physics. He is the associate editor of Frontier of Optolelectronics and a member of the editorial board of Scientific Reports. He is an advisory member of the International Organizing Committee for Infrared, Millimeter and Terahertz Waves. His research interest is in the areas of quantum transport of nanostructures, terahertz photonics, nonlinear dynamics of semiconductors, graphene and topological insulators. He has received several awards induding JSPS Fellow 2001, Norwegian Research Council Senior Fellow 1996, Australian Academy of Sciences International Award 1999, 2000, 2004.