Magneto-Optics of a Weyl Semimetal beyond the Conical Band Approximation: Case Study of TaP

International audienceLandau-level spectroscopy, the optical analysis of electrons in materials subject to a strong magneticfield, is a versatile probe of the electronic band structure and has been successfully used in the identificationof novel states of matter such as Dirac electrons, topological materials or Weyl semimetals. The latter arisefrom a complex interplay between crystal symmetry, spin-orbit interaction, and inverse ordering ofelectronic bands. Here, we report on unusual Landau-level transitions in the monopnictide TaP thatdecrease in energy with increasing magnetic field. We show that these transitions arise naturally atintermediate energies in time-reversal-invariant Weyl semimetals where the Weyl nodes are formed by apartially gapped nodal-loop in the band structure. We propose a simple theoretical model for electronicbands in these Weyl materials that captures the collected magneto-optical data to great extent