点击次数：

COLLOQUIA & SEMINARS 2017:
 

2. (SEMINAR)"Doppler shift picture of the Dzyaloshinskii-Moriya interaction and light propagation in systems with broken inversion symmetry", Prof. Dr. Gen Tatara (RIKEN, JAPAN), at 2:00 pm, June 15, 2017.

1. Abstract:
   We present a physical picture for the emergence of the Dzyaloshinskii-Moriya (DM) interaction based on the idea of the Doppler shift by an intrinsic spin current induced by spin-orbit interaction under broken inversion symmetry such as the case with Rashba interaction1. The picture is confirmed by a rigorous effective Hamiltonian theory, which reveals that the DM coefficient is given by the magnitude of the intrinsic spin current. The expression is directly applicable to first principles calculations and clarifies the relation between the interaction and the electronic band structures. Quantitative agreement with experimental results is obtained for the skyrmion compounds Mn_{1-x}Fe_{x}Ge and Fe_{1-x}Co_xGe. The Doppler shift occurs for incoming electromagnetic wave, too, when the Rashba interaction and magnetization are present, resulting in directional dichroism. The effective Hamiltonian for the electromagnetic field is shown to the vector type, u.(ExB), where u corresponds to the intrinsic velocity due to the troidal moment.

   
   

3. (SEMINAR)"Prediction of Two Dimensional Materials Through Global Optimization", Prof. Dr. Hong-Jun Xiang (Fudan University), at 4:00 pm, September 15, 2017.

1. Abstract:
   In recent years, two-dimensional (2D) or quasi-2D materials have attracted numerous interests for their fascinating properties. It is highly desirable to design new functional 2D materials. A method based on the particle swarm optimization (PSO) algorithm is proposed to design 2D and Q2D materials. With this development, we discover several new functional 2D/Q2D materials: a new 2D semiconducting material C3N, which was recently confirmed experimentally; two hydrogenated materials of layered Si8H2 and Si6H2 possessing quasi-direct band gaps of 0.75 eV and 1.59 eV, respectively, which have potential for the applications in light emitting diode and photovoltaics devices; a new three-layer Q2D Bi4F4 structure, which is a 2D topological insulator with a large band gap (0.69 eV); 2D P4O4 and 2D P2O3 as good candidates for photochemical water splitting and a novel nanoscale multiple-state memory applications, respectively; 2D hexgonal CrN and CrB2 as 2D hyperferroelectric metals.