Lorentz-boost-driven magneto-optics in a Dirac nodal-line semimetal

TL;DR

This paper reveals that in topological Dirac semimetals with dispersive nodal lines, the optical-determined band gap varies with magnetic field orientation due to Lorentz-boost-driven band-gap renormalization, challenging conventional methods.

Contribution

It demonstrates that standard optical methods for measuring band gaps are ineffective in certain topological semimetals because of orientation-dependent effects caused by Lorentz boosts.

Findings

Optical band gap depends on magnetic field orientation.

Lorentz boosts cause band-gap renormalization in Dirac nodal-line semimetals.

Conventional optical methods fail to accurately measure band gaps in these materials.

Abstract

Optical response of crystalline solids is to a large extent driven by excitations that promote electrons among individual bands. This allows one to apply optical and magneto-optical methods to determine experimentally the energy band gap - a fundamental property crucial to our understanding of any solid - with a great precision. Here we show that such conventional methods, applied with great success to many materials in the past, do not work in topological Dirac semimetals with a dispersive nodal line. There, the optically deduced band gap depends on how the magnetic field is oriented with respect to the crystal axes. Such highly unusual behaviour is explained in terms of band-gap renormalization driven by Lorentz boosts.