  The capability of direct photocurrent detection of orbital angular momentum
(OAM) of light has recently been realized with topological Weyl semimetal, but
limited to near infrared wavelength range. The extension of direct OAM
detection to midinfrared, a wavelength range that plays important role in a
vast range of applications, such as autonomous driving, night vision and motion
detection, is challenging and has not yet been realized. This is because most
studies of photocurrent responses are not sensitive to the phase information
and the photo response is usually very poor in the mid-infrared. In this study,
we designed a photodetector based on Type-II Weyl semimetal tantalum iridium
tellurides with designed electrode geometries for direct detection of the
topological charge of OAM through orbital photogalvanic effect. Our results
indicate helical phase gradient of light can be distinguished by a current
winding around the optical beam axis with a magnitude proportional to its
quantized OAM mode number. The topological enhanced response at mid-infrared of
TaIrTe4 further help overcome the low responsivity issues and finally render
the direct orbital angular momentum detection capability in mid-infrared. Our
study enables on-chip integrated OAM detection, and thus OAM sensitive focal
plane arrays in mid-infrared. Such capability triggers new route to explore
applications of light carrying OAM, especially that it can crucially promote
the performance of many mid-infrared imaging related applications, such as
intricate target recognition and night vision.
