We investigate the optoelectronic response of a graphene interface junction,
formed with bilayer and single-layer graphene, by photocurrent (PC) microscopy.
We measure the polarity and amplitude of the PC while varying the Fermi level
by tuning a gate voltage. These measurements show that the generation of PC is
by a photo-thermoelectric effect. The PC displays a factor of ~10 increase at
the cryogenic temperature as compared to room temperature. Assuming the
thermoelectric power has a linear dependence on the temperature, the inferred
graphene thermal conductivity from temperature dependent measurements has a
T^{1.5} dependence below ~100 K, which agrees with recent theoretical
predictions
