Nodal Semimetals: A Survey on Optical Conductivity

Abstract

Among different topological and related phases of condensed matter, nodal semimetals occupy a special place—the electronic band topology in these materials is related to 3D bulk, rather than to surface, states. A great variety of different realizations of electronic band crossings (the nodes) leads to a plethora of different electronic properties, ranging from chiral anomaly to solid-state realizations of a black-hole horizon. The different nodal phases have similar low-energy band structure and quasiparticle dynamics, which both can be accessed experimentally by a number of methods. Optical measurements with their large penetration depth and high energy resolution are ideally suited as such a bulk probe, especially at low energies where other spectroscopic methods often lack the required resolution. Herein, recent optical conductivity studies of different nodal semimetals are reviewed, possible limitations of such measurements are discussed, and a comparison between the experimental results, simple theoretical models, and band-structure-based calculations is provided.