  Andreev interferometers, normal metal wires coupled to superconducting loops,
display phase coherent changes as the magnetic flux through the superconducting
loops is altered. Properties such as the electronic and thermal conductance of
these devices have been shown to oscillate symmetrically about zero with a
period equal to one superconducting flux quantum, $\Phi_o = h/2e$. However, the
thermopower of these devices can oscillate symmetrically or antisymmetrically
depending on the geometry of the sample, a phenomenon not well understood
theoretically. Here we report on thermopower measurements of a double-loop
Andreev interferometer where two Josephson currents in the normal metal wire
may be controlled independently. The amplitude and symmetries of the observed
thermopower oscillations may help to illuminate the unexplained dependence of
oscillation symmetry on sample geometry.
