  Broadband, efficient and fast conversion of light to electricity is crucial
for sensing and clean energy. Here we reveal the largest observed bulk
photo-voltaic effect (BPVE), an intrinsic mechanism predicted to be ultrafast
and exceed the Shockley-Quiesser limit. This discovery results from combining
recent developments in the connection of BPVE to topology, Weyl semimetals and
focused-ion beam fabrication. Our room temperature observation of the first
BPVE in the mid-IR, is enabled by microscopic devices of the Weyl semimetal
TaAs. Detailed symmetry analysis enables unambiguous separation of this
response from competing photo-thermal effects. The size and wavelength range of
the shift current offers new opportunities in optical detectors, clean energy,
and topology, while directly demonstrating the utility of Weyl semimetals for
applications.

Mesoscale and Nanoscale Physics