Landau level spectroscopy as a window into topological semimetals

A strong magnetic field confines band electrons to a discrete set of Landau levels. The material’s band structure is directly linked to the energy spectrum of these Landau levels. With infrared light, we can excite transitions of carriers from one level to another, and these are called inter-Landau level transitions. Since the early 1950s, this technique, known as Landau level spectroscopy, has been widely employed as an extremely sensitive probe of semimetal and semiconductor band structures.

I will give an overview of our recent progress on Landau level spectroscopy of Dirac and Weyl semimetals. Through recent advances, we can resolve intricate complexities of their bands, all while discovering new physics. I will present a new analysis of highly detailed inter-Landau level transition maps in extreme magnetic fields, focusing on select topological materials: Dirac semimetals [1,2], a weak topological insulator ZrTe5 [3,4], and a Weyl semimetal TaAs [5]. I will discuss a novel approach which enables us to further exploit the rich magneto-optical spectra, and gain deeper knowledge of topological semimetals.