  Using a local thermometry technique, we have been able to quantitatively
measure the thermal resistance $R^T$ of diffusive Andreev interferometers. We
find that $R^T$ is strongly enhanced from its normal state value at low
temperatures, and behaves non-linearly as a function of the thermal current
through the sample. We also find that the $R^T$ oscillates as a function of
magnetic flux with a fundamental period corresponding to one flux quantum
$\Phi_0=h/2e$, demonstrating the phase coherent nature of thermal transport in
these devices. The magnitude of $R^T$ is larger than predicted by recent
numerical simulations.
