Wavelength-insensitive and fast photothermoelectric response in magnetic-Weyl-semimetal Co3Sn2S2 crystals

We systematically characterize the photothermoelectric (PTE) effect of pristine and Se-doped (4%, 8%, and 11%) Co3Sn2S2 crystals, a magnetic-Weyl-semimetal, on electromagnetic-wave wavelength and temperature. The photovoltages of these Co3Sn2S2 crystals are insensitive to the electromagnetic-wave wavelength, with 23% variance, in bands ranging from 444 to 1550 nm. Remarkably, the 4%-Se doped Co3Sn2S2 demonstrates the best PTE performance among these samples, yielding a 22.4 mV/W optical responsivity and a short response time (∼100 ms) under 1550 nm illumination. The photovoltage of Co3Sn2S2 nearly monotonically increased with increasing temperature. The theoretical analyses verify that the wavelength-insensitive PTE response of Co3Sn2S2 comes from the nearly same trend of its wavelength-dependent optical refractive index and extinction coefficient, and the best PTE performance of 4%-Se doped Co3Sn2S2 is attributed to the largest product of Seebeck coefficient and electrical conductivity. This work demonstrates that magnetic Weyl semimetals may be promising for infrared photodetection.