“Coulomb interaction effects in topological materials”

Dr. Sang Jun Jeon
Department of Physics, Chung-Ang University

Sep. 24 (Fri.), 02:30 PM
Online seminar
https://kaist.zoom.us/j/88224188486
회의 ID: 882 2418 8486
암호: 080840

Abstract:
Topological materials can be classified into partially gapped (Dirac or Weyl semimetals) or fully gapped (topological insulators) systems. So far, the electronic band structure of the topological materials is based on the symmetry that the material possesses. However, Coulomb interaction effects are significant in forming the band topology when the system is highly correlated due to the high density of states, or the system’s dielectric screening is not efficient. Here I present the experimental signature of Coulomb interactions in a type II Weyl semimetal and a Dirac nodal line semimetal.
MoTe2 is one of the first candidates of type II Weyl semimetals. Its electronic structure was calculated from the first principle and measured with ARPES and STM. However, the size and the shape of the Fermi surface determined from the calculation and the experimental observation show a significant difference. By combining the STM-QPI experiments with the momentum-dependent self-energy corrected calculation (GW approximation), we found that the electron-electron interaction plays a substantial role in forming Weyl fermions in MoTe2.
Dirac nodal line semimetal, SrAs3, whose bulk band crossing line is protected by time-reversal symmetry and inversion symmetry. We observed a global symmetry breaking on a surface of SrAs3 and an impurity-induced symmetry breaking in SrAs3. Due to the vanishing density of states near the Fermi energy and the extremely anisotropic Fermi surface of the nodal ring, the observed charge screening is highly anisotropic with a substantial length scale. I will discuss the role of the long-range Coulomb interaction and possible electron-phonon interaction in SrAs3.