  In a liquid of superconducting vortices, a longitudinal thermal gradient
generates a transverse electric field. This Nernst signal peaks at an
intermediate temperature and magnetic field, presumably where the entropy
difference between the vortex core and the superfluid environment is largest.
There is a puzzling similarity of the amplitude of this peak across many
different superconductors. This peak can be assimilated to a minimum in the
viscosity to entropy density ratio of the vortex liquid. Expressed in units of
$\frac{\hbar}{k_B}$, this minimum is one order of magnitude larger than what is
seen in common liquids. Moreover, the entropy stocked in the vortex core is
\textit{not} identical to the entropy bound to a moving magnetic flux line. Due
to a steady exchange of normal quasi-particles, entropy can leak from the
vortex core. A slowly moving vortex will be peeled off its entropy within a
distance of the order of a superconducting coherence length, provided that the
$\frac{\Delta}{E_F}$ ratio is sufficiently large.
