  Unlocking the vast potential of optical sensing technology has long been
hindered by the challenges of achieving fast, sensitive, and broadband
photodetection at ambient temperatures. In this review, we summarize recent
progress in the study of nonlinear photocurrent in topological quantum
materials, and its application in broadband photodetection without the use of
p-n junction based semiconductor diodes. The intrinsic quadratic transverse
current-input voltage relation is used to rectify the alternating electric
field from incident radio, terahertz or infrared waves into a direct current,
without a bias voltage and at zero magnetic field. We review novel
photocurrents in several material systems, including topological Weyl
semimetals, chiral crystals, ferroelectric materials, and low dimensional
topological insulators. These quantum materials hold tremendous promise for
broadband high-frequency rectification and photodetection, featuring
substantial responsivity and detectivity.
