The topological nature of a material is not only reflected on the surfaces or along the edges but also hidden inside the material in the bulk electronic structure. In this talk, I will describe how the bulk-sensitive magneto-infrared spectroscopy technique can be used to probe the electronic structure topology. I will use transition-metal pentatellurides (ZrTe5, Dirac semimetals) and monopnictides (NbP, Weyl semimetals) as material examples. For ZrTe5, we find that the observed Landau level transitions are similar to that in graphene but with a finite mass and the Zeeman effect opens the inverted band gap due to the large g-factor in the materials. For the NbP, we find that the magnetic field opens a sizable gap at the charge neutrality point (Weyl annihilation) due to the finite coupling between the Weyl points and a new optical transition rule appears when the magnetic field breaks the axial symmetry. For both material systems, a semiquantitative agreement between the experiment and the effective Hamiltonian model calculation is achieved.
Zhigang Jiang is an Associate Professor of Physics at the Georgia Institute of Technology (Georgia Tech). He received his B.Sc. in Physics from Peking University in 1999 and Ph.D. in Physics from Northwestern University in 2005. He joined the faculty at Georgia Tech in 2008, after a joint postdoc experience among Columbia University, Princeton University, and the National High Magnetic Field Laboratory. His areas of research are in electronic transport and magneto-optical studies of quantum materials including graphene, topological insulators, and more recently Dirac and Weyl semimetals. He has authored 50+ research articles in impactful journals such as Nature, Science, Nature Physics, Nature Communications, PRL, JACS, Nano Lett., etc.