  When the Fermi level matches the Dirac point in graphene, the reduced charge
screening can dramatically enhance electron-electron (e-e) scattering to
produce a strongly interacting Dirac liquid. While the dominance of e-e
scattering already leads to novel behaviors, such as electron hydrodynamic
flow, further exotic phenomena have been predicted to arise specifically from
the unique kinematics of e-e scattering in massless Dirac systems. Here, we use
optoelectronic probes, which are highly sensitive to the kinematics of electron
scattering, to uncover a giant intrinsic photocurrent response in pristine
graphene. This photocurrent emerges exclusively at the charge neutrality point
and vanishes abruptly at non-zero charge densities. Moreover, it is observed at
places with broken reflection symmetry, and it is selectively enhanced at free
graphene edges with sharp bends. Our findings reveal that the photocurrent
relaxation is strongly suppressed by a drastic change of fast photocarrier
kinematics in graphene when its Fermi level matches the Dirac point. The
emergence of robust photocurrents in neutral Dirac materials promises new
energy-harvesting functionalities and highlights intriguing electron dynamics
in the optoelectronic response of Dirac fluids.
