Optical Signatures of Dirac Nodal-lines in NbAs$_2$

TL;DR

This study reveals optical signatures of Dirac nodal-lines in NbAs$_2$, demonstrating their universal electrodynamics, the effects of spin-orbit interaction, and their relation to magneto-resistance through polarized optical and magneto-optical spectroscopy.

Contribution

It provides experimental and theoretical evidence of Dirac nodal-line signatures in NbAs$_2$, including energy gaps, linear optical conductivity, and surface states, advancing understanding of topological semimetals.

Findings

Energy gaps along nodal-lines due to spin-orbit interaction

Linear optical conductivity scaling as $\sigma_1 (\omega) o\omega$

Magneto-optical data confirms massive Dirac nature and surface states

Abstract

Using polarized optical and magneto-optical spectroscopy, we have demonstrated universal aspects of electrodynamics associated with Dirac nodal-lines. We investigated anisotropic electrodynamics of NbAs$_2$ where the spin-orbit interaction triggers energy gaps along the nodal-lines, which manifest as sharp steps in the optical conductivity spectra. We show experimentally and theoretically that shifted 2D Dirac nodal-lines feature linear scaling $\sigma_1 (\omega)\sim\omega$, similar to 3D nodal-points. Massive Dirac nature of the nodal-lines are confirmed by magneto-optical data, which may also be indicative of theoretically predicted surface states. Optical data also offer a natural explanation for the giant magneto-resistance in NbAs$_2$.