  A non-local Hall bar geometry is used to detect neutral-current Hall effects
in graphene on silicon dioxide. Disorder is tuned by the addition of Au or Ir
adatoms in ultra-high vacuum. A reproducible neutral-current Hall effect is
found in both as-fabricated and adatom-decorated graphene. The Hall angle
exhibits a complex but reproducible dependence on gate voltage and disorder,
and notably breaks electron-hole symmetry. An exponential dependence on length
between Hall and inverse-Hall probes indicates a neutral current relaxation
length of approximately 300 nm. The short relaxation length and lack of
precession in parallel magnetic field suggest that the neutral currents are
valley currents. The near lack of temperature dependence from 7-300 K is
unprecedented and promising for using controlled disorder for room temperature
neutral-current electronics.
