  We have measured the diffusion thermopower of a quantum Hall system in a
Corbino setup. A concentric electron-temperature gradient is introduced by
irradiating microwaves, via a coplanar waveguide, near the outer rim of a
circular mesa of a two-dimensional electron gas. The resulting radial
thermovoltages exhibit sawtooth-like oscillations with the magnetic field,
taking large positive (negative) values just below (above) integer fillings
with sign reversal at the center of the quantum Hall plateaus. The behavior is
in agreement with a recent theory [Y. Barlas and K. Yang: Phys. Rev. B 85
(2012) 195107], which treats disorder within the self-consistent Born
approximation.
