School of Physics Thesis Dissertation Defense

Presenter:       Tianhao Zhao

Title:                Magneto-Infrared Spectroscopy on ZrTe5 and Non-polar Epitaxial Graphene

Date:               Wednesday, January 24, 2024

Time:               12:00 p.m.

Location:        Howey N202/202

Committee members:

Dr. Zhigang Jiang, School of Physics, Georgia Institute of Technology, Advisor

Dr. Walter A. de Heer, School of Physics, Georgia Institute of Technology

Dr. Phillip N. First, School of Physics, Georgia Institute of Technology

Dr. Hailong Wang, School of Physics, Georgia Institute of Technology

Dr. Sidong Lei, Department of Physics and Astronomy, Georgia State University

Abstract:

We use magneto-infrared spectroscopy to study zirconium pentatelluride (ZrTe5) and non-polar epitaxial graphene. ZrTe5 is a 3D topological material residing on the boundary of the strong and weak topological phase. By fitting the data to kp model, we find the band parameters of ZrTe5 strongly isotropic along its three principal axes. We identify two sets of Landau level transitions in the low-temperature magneto spectra, which signifies a second extremum in the band structure resulting from the band inversion. We conclude the material to be in the strong topological phase in the low-temperature range. Temperature-dependent measurements are also performed on ZrTe5 and the massive Dirac model is used to fit the data. We find that the band gap has a monotonic increasing behavior to the temperature. We explain the observation with a topological phase transition scenario without band gap closing. In the second part, non-polar epitaxial graphene is grown on the non-polar facet of silicon carbide. In its magneto spectra, We observe monolayer graphene behavior with band parameters consistent with previously reported epigraphene. Besides that, peak splittings at high magnetic fields are observed. We attribute it to the Landau level splitting effect in the twisted bilayer graphene when the energy is above van Hove's singularity. We fit the data with the continuum model and extract the information on the rotation angle and the interlayer coupling.