Title:Exotic response in topological materials

Speaker:Zhou Li, RIKEN

Date:2018-08-02 10:30

Venue:C302 Lecture Hall, New Science Building


Abstract:The 2016 nobel prize in physics was awarded to topological phase transitions and topological phase of matter. In this talk I will briefly review the BKT topological transition of vortex and anti-vortex states and the TKNN formula in the explanation of the quantization of Hall conductivity. We use the Green's function technique and Kubo formula to study the spectral function, density of states, optical and magneto-optical conductivity in topological insulators and valleytronic materials. In general the Kubo formula can also be generalized to study nonlinear response to the external driving electro-magnetic field E or B. One example was given in our study of the nonlinear magneto-optical conductivity for topological insulators in which the particle-hole asymmetry can generate chiral absorption of left and right circularly polarized light. Recently we study the nonlinear response (frequency up- and down-conversion) to an electric field E and found an unusual way to generate a DC current from frequency down-conversion. This may bring novel nonlinear thermoelectric functionalities (e.g. thermal energy harvesting) in the far-infrared region. We also studied the time evolution of a Gaussian wave packet in a flat-band system with disorder-induced depasing and decay of quantum states.