Mid-infrared photoresponse of RAlGe (R=La, Ce, Pr) Weyl magnets

Mid-infrared photoresponse measurements offer an alternative but unique approach to studying the chiral anomaly in Weyl semimetals by selectively exciting Weyl fermions with circularly polarized light. Here, we selected rare-earth-based magnetic Weyl semimetals RAlGe (R = La, Ce, Pr) as the best candidate to investigate helicity-dependent photoresponse because they offer rich topological tunability. This system offers a diverse platform for systematically studying chiral fermions under the influence of magnetism and at many different Weyl band positions relative to the Fermi level. For example, the Weyl band structures of nonmagnetic LaAlGe and slightly magnetic CeAlGe are similar, but that of ferromagnetic PrAlGe is quite different. Moreover, PrAlGe has type-I Weyl bands near the Fermi level, whereas LaAlGe and CeAlGe exhibit type-I Weyl bands far above the Fermi level. We employed a 10.6-micron mid-infrared CO2 laser, which is sufficiently low energy to excite Weyl fermions in Weyl bands near the Fermi level. We investigated temperature- and circular polarization-dependent photoresponse in RAlGe. We also explored the influence of in-plane magnetic fields on the photoresponse, which may provide a selective excitation of Weyl fermions.