Lorentz-Boost-Driven Magneto-Optics in a Dirac Nodal-Line Semimetal

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 it is shown 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 behavior is explained in terms of band-gap renormalization driven by Lorentz boosts which results from the Lorentz-covariant form of the Dirac Hamiltonian relevant for the nodal line at low energies.

Automated summary

The optical response of crystalline solids is affected by excitations that promote electron transitions between energy bands. Optical and magneto-optical methods have been used to experimentally determine the energy band gap, a fundamental property of solids. However, these conventional methods do not work for topological Dirac semiconductors with a dispersive nodal line. This unusual behavior can be explained by band-gap renormalization driven by Lorentz boosts.