Magneto-Optics of the Weyl Semimetal TaAs in the THz and IR Regions

TL;DR

This study investigates the magnetic-field-dependent optical properties of the Weyl semimetal TaAs in the THz and IR regions, revealing distinct band dispersions and Landau level behaviors.

Contribution

It provides the first detailed experimental analysis of magnetic-field effects on optical spectra in TaAs, highlighting the crossover from Dirac to parabolic bands.

Findings

Landau level gap increases with 

THz spectra scale with  and 1/

IR peaks suggest parabolic band behavior

Abstract

The magnetic-field dependence of optical reflectivity [$R(\omega)$] and optical conductivity [$\sigma(\omega)$] spectra of the ideal type-I Weyl semimetal TaAs has been investigated at the temperature of 10 K in the terahertz (THz) and infrared (IR) regions. The obtained $\sigma(\omega)$ spectrum in the THz region of $\hbar\omega\leq15$ meV is strongly affected by the applied magnetic field ($B$): The Drude spectral weight is rapidly suppressed and an energy gap originating from the optical transition in the lowest Landau levels appears with a gap size that increases in proportion to $\sqrt{B}$, which suggests linear band dispersions. The obtained THz $\sigma(\omega)$ spectra could be scaled not only in the energy scale by $\sqrt{B}$ but also in the intensity by $1/\sqrt{B}$ as predicted theoretically. In the IR region for $\hbar\omega\geq17$ meV, on the other hand, the observed $R(\omega)$ peaks originating from the optical transitions in higher Landau levels are proportional to linear-$B$ suggesting parabolic bands. The different band dispersions originate from the crossover from the Dirac to the free-electron bands.