CPM Seminar

Probing Dirac fermions in correlated electron materials via magneto-infrared spectroscopy

Zhigang Jiang

School of Physics
Georgia Institute of Technology

The overarching goal of my research program is to understand the energy, symmetry and dispersion of low-lying excitations in correlated electron materials via magneto-optical spectroscopy. In this talk, I will first review our previous effects in studying Dirac fermions in graphene and HgTe quantum wells and then report the observation of massive Dirac fermions in transition-metal pentatelluride ZrTe₅ and HfTe₅.

ZrTe₅ has recently attracted much interest due to the possibility of hosting a large-gap quantum spin Hall insulator in its monolayer form. However, its electronic structure in the bulk is currently under heated debate, with interpretations ranging from weak/strong topological insulator to Dirac semimetal. Using bulk-sensitive magneto-infrared spectroscopy, we show that the charge carriers in ZrTe₅ thin flakes are graphene-like and exhibit a quasi-2D behavior. In a magnetic field, we observe a series of inter-band Landau level (LL) transitions that can be described by a massive Dirac fermion model with a small relativistic mass. More interestingly, we observe a four-fold splitting of low-lying LL transitions. Thanks to the newly developed circular polarized magneto-infrared capability, we are able to separate the σ+ and σ- active transitions. These observations enable further exploration of the origin in the splitting: (i) the band asymmetry breaks the two-fold degeneracy of the dipole allowed inter-band LL transitions, and (ii) the remaining two-fold splitting is due to the lifting of the spin degeneracy caused by a combined effect of large g-factor and finite Dirac mass. Our results support a 2D Dirac semimetal interpretation, consistent with electronic transport studies.