Mid-infrared anomalous Hall measurement in PrAlGe magnetic Weyl semimetal

Weyl semimetals have a quasi-particle excitation called Weyl fermions, which appear in a material with two non-degenerate bands crossing near Fermi level in three-dimensional momentum space. Low-energy excitation at two band crossing points is called Weyl points. The pairs of Weyl points produce a large Berry curvature contributing to the intrinsic anomalous Hall conductivity. Here, we report mid-infrared anomalous Hall conductivity in PrAlGe magnetic Weyl semimetal in proximity to the Fermi level at 70 meV – 200 meV with applying magnetic field below 1T and temperatures of 4 K – 300 K. PrAlGe shows ferromagnetic ordering below 0.4T at below 15 K. The magnetic Weyl semimetals show the magnetic field control of the Weyl point positions in momentum space emerging large intrinsic anomalous Hall conductivity at low-energy band below 100 meV. We develop custom-built broadband magneto-optical spectroscopy system at mid-infrared spectral range which utilizes a double modulation from a Fourier-transform infrared spectrometer and photoelastic modulator. Polarization rotation and ellipticity angle spectrums of PrAlGe in Kerr geometry are measured. We convert Kerr angle to Hall angle by using optical conductivity obtained from reflection spectrum measurement with Kramers-Kronig analysis.