Optical conductivity signatures of open Dirac nodal lines

TL;DR

This study explores the optical and magneto-optical properties of BaNiS₂, revealing signatures of Dirac nodal lines and their universal topological features through experimental measurements and first-principles calculations.

Contribution

It provides the first detailed analysis of optical conductivity signatures associated with Dirac nodal lines in BaNiS₂, highlighting their universal topological characteristics.

Findings

Landau levels show √B behavior along the nodal line

Optical conductivity has a temperature-independent isosbestic line

First-principles calculations link the isosbestic line to Dirac nodal state transitions

Abstract

We investigate the optical conductivity and far-infrared magneto-optical response of BaNiS$_2$, a simple square-lattice semimetal characterized by Dirac nodal lines that disperse exclusively along the out-of-plane direction. With the magnetic field aligned along the nodal line the in-plane Landau level spectra show a nearly $\sqrt{B}$ behavior, the hallmark of a conical-band dispersion with a small spin-orbit coupling gap. The optical conductivity exhibits an unusual temperature-independent isosbestic line, ending at a Van Hove singularity. First-principles calculations unambiguously assign the isosbestic line to transitions across Dirac nodal states. Our work suggests a universal topology of the electronic structure of Dirac nodal lines.