Magneto-optical response of the Weyl semimetal NbAs: Experimental results and hyperbolic-band computations

The magneto-optical properties of (001)-oriented NbAs single crystals have been studied in the spectral range
from 5 to 150 meV and in magnetic fields of up to 13 T. A rich spectrum of inter-Landau-level transitions is
revealed by these measurements. The transitions follow a square-root-like dependence with magnetic field, but
the simple linear-band approximation is unable to accurately reproduce the observed behavior of the transitions
in applied fields. We argue that the detected magneto-optical spectra should be related to crossing hyperbolic
bands, which form the W1 cones. We propose a model Hamiltonian, which describes coupled hyperbolic bands
and reproduces the shape of the relevant bands in NbAs. The magneto-optical spectra computed from this
Hamiltonian nicely reproduce our observations. We conclude that the hyperbolic-band approach is a minimal
model to adequately describe the magneto-optical response of NbAs and that the chiral (conical) bands do not
explicitly manifest themselves in the spectra.