Kagome magnet TbMn6βSn6β is a new type of topological material that is
known to support exotic quantum magnetic states. Experimental work has
identified that TbMn6βSn6β hosts Dirac electronic states that could lead to
topological and Chern quantum phases, but the optical response of the Dirac
fermions of TbMn6βSn6β and its properties remain to be explored. Here, we
perform optical spectroscopy measurement combined with first-principles
calculations on single-crystal sample of TbMn6βSn6β to investigate the
associated exotic phenomena. TbMn6βSn6β exhibits a frequency-independent
optical conductivity spectra in a broad range from 1800 to 3000 cmβ1
(220-370 meV) in experiments. The theoretical band structures and optical
conductivity spectra are calculated with several shifted Fermi energy to
compare with the experiment. The theoretical spectra with 0.56 eV shift for
Fermi energy are well consistent with our experimental results. Besides, the
massive quasi-two-dimensional (quasi-2D) Dirac bands, which have linear band
dispersion in kxβ-kyβ plane and no band dispersion along the kzβ
direction, exist close to the shifted Fermi energy. According to tight-bond
model analysis, we find that quasi-2D Dirac bands give rise to a flat optical
conductivity, while its value is smaller than the result by calculations and
experiments. It indicates that the other trivial bands also contribute to the
flat optical conductivity