Nernst effect in the phase-fluctuating superconductor InO_x

We present a study of the Nernst effect in the amorphous 2D superconductor InO_x, whose low carrier density implies low phase rigidity and strong superconducting phase fluctuations. Instead of presenting the abrupt jump expected at a BCS transition, the Nernst signal evolves continuously through the superconducting transition as previously observed in underdoped cuprates. This contrasts with the case of Nb_0.15Si_0.85, where the Nernst signal due to vortices below T_c and by Gaussian fluctuations above are clearly distinct. The behavior of the ghost critical field in InO _x points to a correlation length which does not diverge at T _c, a temperature below which the amplitude fluctuations freeze, but phase fluctuations survive.