Nernst effect in the phase-fluctuating superconductor InOx

We present a study of the Nernst effect in the amorphous 2D superconductor InOx, 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 Nb0.15Si0.85, where the Nernst signal due to vortices below Tc and by Gaussian fluctuations above are clearly distinct. The behavior of the ghost critical field in InOx points to a correlation length which does not diverge at Tc, a temperature below which the amplitude fluctuations freeze, but phase fluctuations survive.