Time：Friday, March 18, 10:30 - 11:30

Venue: BAQIS meeting room 526

Title：Unconventional excitonic states in layered SiP2 and the dynamic tuning in the quantum topological materials

Host：Qihua Xiong, Research Scientist, BAQIS; Professor, Tsinghua University. 

Abstract：Many-body interactions between quasiparticles (electrons, excitons and phonons) have led to the emergence of new complex correlated states and are at the core of condensed matter physics and material science. In this talk, we systemically demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP2), in which the bound electron-hole pair is composed of electrons confined within one-dimensional phosphorus–phosphorus chains and holes extended in two-dimensional SiP2 layers. The excitonic state and the emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Within the GW plus Bethe–Salpeter equation calculations and solving the generalized Holstein model non-perturbatively, we confirm that the observed sideband feature results from the correlated interaction between excitons and optical phonons. Furthermore, we show the excitonic states could be tuned via layer stacking in SiP2. In the second part, I will focus on the emergence of new phenomena and the related topological properties in non-equilibrium, including the light induced anomalous Hall effect in graphene and topological phase transition driven by nonlinear phononic coupling.

About the Speaker：Dr. Peizhe Tang obtained his B.Sc. from Lanzhou University in 2009, and received his Ph.D. degree in Physics from Tsinghua Unviersity under the supervision of CAS Academician Professor Wenhui Duan. From 2015-2017, he pursued his postdoctoral research in collaboration with Professor Shouchen Zhang. He then moved to Max Planck Institute for The Structure and Dynamics of Matter to pursue his second postdoctoral research experiences with Professor Angel Rubio from 2017-2018. In April 2018, he was awarded the prestigous Marie-Curie Fellowship. He received national young talent programme in 2019 and joined School of Materials Sciences and Engineering of Beihang University. Dr Tang's research is specialized in numerical simulation of electronic band structures and topological properties of condensed matter, and their nonequilibrium dynamics. He has published more than 30 peer-reviewed articles in well-established journals including Science, Nature Physics, Nature Nanotechnology, Physical Review Letters, etc., with a total citation of >3,500 times.