Very Long Wave Infrared Photocurrent Response of Magnetic Weyl Semimetal Co 3 Sn 2 S 2

ABSTRACT Weyl semimetals have emerged as promising candidates for broadband photodetection due to their gapless electronic structure and unique topological properties that can enhance the photoresponse for low energy photon. Among them, the ferromagnetic Weyl semimetal Co 3 ;Sn 2 S 2 exhibits exceptional magneto‐optical responses, making it particularly attractive for very long‐wavelength infrared (VLWIR) detection. Here, we systematically investigate the photoresponse mechanisms of Co 3 ;Sn 2 S 2 under typical VLWIR at 14‐µm excitation using scanning photocurrent microscopy. Our results reveal a dual photocurrent response mechanisms governing VLWIR detection in Co 3 ;Sn 2 S 2 . At room temperature, the photocurrent is dominated by the thermoelectric effect at the contact interface, arising from the Seebeck coefficient difference between Co 3 ;Sn 2 S 2 and metal electrodes. Below 100 K, the photoresponse arises from anomalous photo‐Nernst effect at the edges of Co 3 ;Sn 2 S 2 shifts the photocurrent distribution toward the sample edges. Furthermore, we observe a distinct circular polarization dependence of the photocurrent at low temperatures, indicative of an imbalanced generation of chiral‐polarized Weyl fermions. Our work not only elucidates the interplay between thermoelectric and topological effects in Co 3 ;Sn 2 S 2 but also demonstrates its potential for developing tunable VLWIR photodetectors that leverage both thermal and magnetic degrees of freedom.