Mid-infrared helicity-dependent photovoltaic response of PrAlGe across the ferromagnetic phase transition

While most experiments to observe chiral effects in Weyl semimetals rely on measuring a longitudinal negative magnetoresistance in DC transport, optical approaches offer potential advantages. Optical methods could allow for the selective excitation of chiral fermions in Weyl bands, providing another avenue to study its chiral anomaly effect. In this work, we optically investigated a helicity-dependent photovoltaic response of a single-crystal PrAlGe, a magnetic Weyl semimetal, showing two type-I Weyl bands near Fermi level under the ferromagnetic ordering temperature of 15 K. The ferromagnetism induces momentum shift of Weyl points and results in a non-zero Chern number. We measured the mid-infrared photovoltaic response using circularly polarized light with an energy of around 120 meV. The electrically contacted sample is cooled in a magneto-optical cryostat, allowing for temperature and magnetic field-dependent photoresponse measurements. Below 15 K, the helicity-dependent photovoltage shows double dips at left- and right-handed circularly polarized light. We also studied the helicity-dependent photovoltage under in-plane magnetic fields, which results in a selective excitation of chiral electrons by Pauli blocking.