【报告题目】 Theory of Magnetoresistance in Three-Dimensional Dirac Materials
【报 告 人】 Prof. Shun-Qing Shen
Department of Physics, The University of Hong Kong
【时 间】 2019-12-11 4:00 pm (Wedensday)
【地 点】 北园106报告厅
【报告摘要】
Recently, negative longitudinal magnetoresistance has been observed in most topological Dirac/Weyl semimetals, and some other topological materials. I will present the magneto-transport theory for topological Dirac materials in the semi-classical regime and quantum interference regime. In a semi-classical regime, it is shown that the longitudinal magnetoresistance is negative and quadratic of a weak field B while the in-plane transverse magnetoresistance is positive and quadratic of B. The relative magnetoresistance is inversely quartic of the Fermi wave vector and only determined by the density of charge carriers, irrelevant to the external scatterings in the weak scattering limit. This intrinsic anisotropic magnetoresistance is measurable in systems with lower carrier density and high mobility. In the quantum interference regime, a formula of magnetoconductivity is presented for massless and massive Dirac fermions in Dirac materials due to quantum interference of Dirac fermions in scalar impurity scattering potentials. It reveals a striking crossover from positive to negative magneto-resistivity, uncovering strong competition between weak localization and weak antilocalization in multiple Cooperon modes at different chemical potentials, effective masses and finite temperatures. The work sheds light on the important role of strong coupling of the conduction and valence bands in the quantum interference transport in topological nontrivial and trivial Dirac materials.
References:
B. Fu, H. W. Wang, and S. Q. Shen, Quantum diffusive magneto-transport in Dirac materials with chiral symmetry breaking, arXiv: 1909.09297
B. Fu, H. W. Wang, and S. Q. Shen, Quantum interference theory of magnetoresistance in Dirac materials, Phys. Rev. Lett. 122, 246601 (2019)
H. W. Wang, B. Fu, and S. Q. Shen, Intrinsic magnetoresistance in three-dimensional Dirac materials, Phys. Rev. B 98, 081202(R) (2018)
H. Li, H. W. Wang, H. T. He, J. N. Wang, and S. Q. Shen, Giant anisotropic magnetoresistance and planar Hall effect in Dirac semimetal Cd3As2, Phys. Rev. B 97, 201110(R) (2018)
H. Z. Lu and S. Q. Shen, Quantum transport in topological semimetals under magnetic fields, Frontiers of Physics 12, 127201 (2017)
【报告人简介】 Professor Shun-Qing Shen is a professor of physics in Department of Physics, The University of Hong Kong. He is an expert in the field of condensed matter physics, distinguished for his research works on topological insulator, transport theory of topological materials, spintronics of semiconductors, quantum magnetism and orbital physics in transition metal oxides, and novel quantum states of condensed matters. He proposed topological Anderson insulator, spin transverse force, resonant spin Hall effect and theory of phase separation in colossal magnetoresistive (CMR) materials. He developed the theory of weak localization and weak antilocalization in Dirac electrons in the surface states and topological materials. He has published a single-authored monograph, Topological Insulators (Springer, 1st ed., 2012; 2nd ed., 2017), which is the first book on the topic.
Professor Shen received his BS, MS, and PhD in theoretical physics from Fudan University in Shanghai. He was a postdoctorial fellow (1992 – 1995) in China Center of Advanced Science and Technology (CCAST), Beijing, Alexander von Humboldt fellow (1995 – 1997) in Max Planck Institute for Physics of Complex Systems, Dresden, Germany, and JSPS research fellow (1997) in Tokyo Institute of Technology, Japan. In December 1997 he joined Department of Physics, The University of Hong Kong.
Professor Shen received his BS, MS, and PhD in theoretical physics from Fudan University in Shanghai. He was a postdoctorial fellow (1992 – 1995) in China Center of Advanced Science and Technology (CCAST), Beijing, Alexander von Humboldt fellow (1995 – 1997) in Max Planck Institute for Physics of Complex Systems, Dresden, Germany, and JSPS research fellow (1997) in Tokyo Institute of Technology, Japan. In December 1997 he joined Department of Physics, The University of Hong Kong.
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