  Anomalously large thermopower of mesoscopic normal-metal/superconductor
interferometers has been investigated by Chandrasekhar et al. It was shown
that, depending on the geometry of the interferometer, the thermopower is
either symmetric or antisymmetric periodic function of the magnetic flux. We
develop a detailed theory of the observed thermoelectric phenomena in the
framework of the non-equilibrium quasiclassical approach. In particular we
provide, for the first time, a possible explanation of the symmetric
thermopower oscillations. This effect is attributed to the electron-hole
symmetry violation that originates in the steady-state charge imbalance between
different arms of the interferometer. Our theory can be tested by an additional
control over the charge imbalance in a modified setup geometry. We also predict
a sign reversal behavior of the thermopower with increasing temperature that is
consistent with the experiments by Parsons et al.
