  We propose a method for broadband long-wavelength photodetection using the
nonlinear Hall effect in non-centrosymmetric quantum materials. The inherently
quadratic relation between transverse current and input voltage at zero
magnetic field is used to rectify the incident terahertz or infrared electric
field into a direct current, without invoking any diode. Our photodetector
operates at zero external bias with fast response speed and has zero threshold
voltage. Remarkably, the intrinsic current responsivity due to Berry curvature
mechanism is a material property independent of the incident frequency or the
scattering rate, which can be evaluated from first-principles electronic
structure calculations. We identify the Weyl semimetal NbP for terahertz
photodection with large current responsivity reaching $\sim 1$A/W without
external bias.
