Nonmonotonic wavelength dependence of the polarization-sensitive infrared photoresponse of an anisotropic semimetal

Layered semimetals with in-plane anisotropy are promising for advanced polarization-sensitive infrared detection. The investigation of the polarization-dependent photoresponse of semimetals over the whole visible-to-long-wave-infrared range and revealing the physical connection between their optoelectronic properties, optical properties, and electronic band structures is required, but there have been very few studies of this kind. In this work, we conducted a thorough investigation on the polarization-dependent infrared photoresponse of WTe₂ over the visible-to-long-wave-infrared range and discovered a textbook-like perfect consistency between the wavelength-dependent polarization-sensitive photoresponse and the anisotropic dielectric constant mainly affected by interband transitions near the Weyl point. It is revealed that the polarization sensitivity and the responsivity both vary non-monotonically with the wavelength. This phenomenon is attributed to the polarization selective excitation of interband transitions associated with asymmetrically distributed electron orbitals around the Weyl points. Concerning the infrared detection properties of WTe₂, a maximum responsivity of 0.68 mA W^-1 is obtained under self-powered operation. The power dependence of the photoresponse is linear, and the response time is around 14 μs. This work would provoke further studies about the anisotropic photoresponse associated with the transitions even closer to the Dirac or Weyl points, and it provides an approach to select the right semimetal for the right wavelength range of infrared polarization detection.