Temperature-Dependent Photovoltaic Study in Magnetic Weyl Semimetal PrAlGe

Magnetic Weyl semimetal PrAlGe has two type-I Weyl bands near the fermi level under the ferromagnetic ordering at a temperature below 15 K. The ferromagnetism induces momentum shift of Weyl points and results in a non-zero topological number. The chiral nature of Weyl fermions can be detected by measuring the photoresponse induced by circularly polarized mid-infrared light. In this study, we investigated the temperature-dependent photovoltaic response in PrAlGe to understand any photothermal effects before measuring the chiral-dependent photoresponse. We develop a photovoltaic response measurement setup using a 9.2-micron mid-infrared quantum cascade laser with 18 mW power. The sample is housed within a continuous-flow helium cryostat, which reaches a temperature of 9 K. The sample was mounted on a printed circuit board with six gold contact wires. The photovoltaic response of a pair of contacts was measured as a function of temperature and chopper frequency, with light focused on one of them. A temperature gradient across two contacts generates a photovoltaic effect. The photothermal response linearly decreased until a sharp increase near 15 K, coinciding with the Curie temperature of PrAlGe.