  The observation of a large Nernst signal $e_N$ in an extended region above
the critical temperature $T_c$ in hole-doped cuprates provides evidence that
vortex excitations survive above $T_c$. The results support the scenario that
superfluidity vanishes because long-range phase coherence is destroyed by
thermally-created vortices (in zero field), and that the pair condensate
extends high into the pseudogap state in the underdoped (UD) regime. We present
a series of measurements to high fields $H$ which provide strong evidence for
this phase-disordering scenario.
