<注：本视频仅用于学术交流，版权归报告人所有>
►【“凝聚态物理-中关村论坛”第385次讲座】
报告题目：Theory of Magnetoresistance in Three-Dimensional Dirac Materials
报 告 人：Prof. Shun-Qing Shen（沈顺清）
Department of Physics, The University of Hong Kong
报告时间：2019年12月12日（星期四）上午10:00
报告地点：中科院物理研究所M楼236会议室
报告人简介：
沈顺清教授，获复旦大学理论物理专业博士学位，1992-1995年在中国高等科学技术中心博士后，1995-1997年马普复杂物理系统研究所（Max Planck Institute for Physics of Complex Systems）洪堡基金研究员（Alexander von Humboldt fellow），1997年日本东京工业大学（Tokyo Institute of Technology）JSPS研究员（JSPS research fellow）。1997年12月至今，香港大学物理系教授。沈顺清教授在凝聚态物理学领域做出了很多贡献。他预言了拓扑安德森绝缘体（topological Anderson insulator）、自旋横向力（spin transverse force）、共振自旋霍尔效应（resonant spin Hall effect），证明了巡游电子系统反铁磁长程序和非对角长程序的存在性。2010年获得香港“裘槎优秀科研者奖（Croucher Senior Research Fellows）”，2012年出版专著《拓扑绝缘体》（Topological Insulators）。
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)