Chiral pumping at THz frequencies in Weyl semimetal TaAs*

An optical conductivity enhancement is observed at THz frequencies with polarization parallel to an
applied magnetic field. The effect is studied in single crystal TaAs samples utilizing FTIR spectroscopy in
static magnetic fields in the Voigt geometry. The enhanced conductivity, most clearly observed with
fields oriented parallel to either the a- or c- crystal axis, is understood in the context of Weyl state chiral
pumping. Results from applied magnetic fields up to 8T that span the semi-classical and quantum limits
in both kinds of Weyl states are compared to theoretical predictions. Magnetic field dependent
scattering rates in both regimes and geometrical Fermi surface considerations will also be discussed. The
Landau level spectrum of the Weyl states are measured in the E⊥B Voigt geometry and analyzed within
a model of Weyl state pairs, allowing extraction of conduction-valence band asymmetries and the
Lifshitz gap energy.