Abstract:
Topological quantum solids are a new class of systems that behave as an insulator or semimetal in the bulk but whose surface contains conducting states. Starting a decade ago from the original proposal on the principal existence of such state of matter in the case of 2-D called a quantum spin Hall insulator and its subsequent extension to its 3-D analog called a topological insulator, the field has been recently enriched by the discoveries of new topological phases such as topological crystalline insulators, Weyl semimetals, Dirac semimetals, and nodal line semimetals. Their unusual properties such as robust surface currents insensitive to the disorder or various forms of quantum Hall effects have led to a plethora of proposals for the use of topological materials in fundamental research spanning from magnetic monopoles to Majorana fermions, and in applications such as spintronic devices or fault-tolerant quantum computations.
In this talk I will overview some of the most exotic properties such as topologically protected surface states in a form of massless Dirac fermions in topological insulators and Fermi arcs in Weyl semimetals. Charge and spin currents in these systems will be studied where we will show that an external electric field creates a flow of spins through the bulk of a topological insulator to their top and bottom surfaces. We will introduce a counterintuitive idea of increase in nonmagnetic impurity concentration in order to preserve such surface spin accumulation. Next, studies of a Weyl semimetal model will be discussed and contrasted to the case of topological insulator. In particular, we find that robustness to surface disorder can be reached for a straight Fermi arc geometry. This produces conductivities at the surface of Weyl semimetals that are one to two orders of magnitude larger of a comparable set up with surface states of topological insulators.
Brief Bio:
Professional Preparation
1986, MS, Moscow Engineering Physics Institute, Moscow, Russia.
1994. PhD, Lebedev Physical Institute, Moscow, Russia.
1995-1999. Postdoctoral research, Max-Planck Institute, Stuttgart, Germany.
1999-2001. Postdoctoral research, Rutgers University, Piscataway, New Jersey.
Appointments
Since 2008. Professor, Department of Physics, University of California, Davis, CA.
2005-2008. Associate professor, Department of Physics, University of California, Davis, CA.
2001-2005. Assistant professor, Department of Physics, New Jersey Institute of Technology, Newark, New Jersey.
Five recent publications most closely related to the project
1. Sergey Y. Savrasov, Giacomo Resta, Xiangang Wan, Local Self-Energies for V and Pd Emergent from a Non-Local LDA+FLEX Implementation, arXiv:1802.02471.
2. Yongping Du and Er-Jun Kan, Hu Xu, Sergey Y. Savrasov, Xiangang Wan, Turning Copper Metal into Weyl Semimetal, arXiv:1801.06248.
3. Giacomo Resta, Shu-Ting Pi, Xiangang Wan, Sergey Y. Savrasov, High Surface Conductivity of Fermi Arc Electrons in Weyl semimetals, Phys. Rev. B 97, 085142 (2018).
4. Yongping Du, Xiangyan Bo, Di Wang, Er-jun Kan, Chun-Gang Duan, Sergey Y. Savrasov, Xiangang Wan, Emergence of Topological Nodal Lines and Type II Weyl Nodes in Strong Spin--Orbit Coupling System InNbX2(X=S,Se), Phys. Rev. B 96, 235152 (2017).
5. Yongping Du, Feng Tang, Di Wang, Li Sheng, Er-jun Kan, Chun-Gang Duan, Sergey Y. Savrasov and Xiangang Wan, CaTe: a new topological node-line and Dirac semimetal, NPJ Quantum Materials 2, Article 3 (2017).