Speaker: David Cobden, Department of Physics, University of Washington, Seattle
Time: October 29, 2015, 2:00 - 3:00
Scanning photocurrent measurements provide a powerful means of studying the spatially resolved optoelectronic and electrical properties of a device. In graphene devices in a perpendicular magnetic field we observe photocurrent generated uniformly along the free edges, with opposite sign at opposite edges. The signal is antisymmetric in field, shows a peak versus gate voltage at the neutrality point flanked by wings of opposite sign at low fields, and exhibits quantum oscillations at higher fields. These features are all explained by the Nernst effect associated with a local electron temperature rise induced by the laser. This photo-Nernst effect provides an unambiguous demonstration of the Shockley-Ramo nature of long-range photocurrent generation in a gapless material like graphene. It also provides a sensitive means of investigating quasiparticle properties and edge states in simple two-terminal devices.