Direct test of pairing fluctuations in the pseudogap phase of an underdoped cuprate

We report on a direct test of pairing fluctuations in the pseudogap regime of underdoped superconducting cuprates using a Josephson junction. In this experiment, the coupling between a rigid superconducting pair field and pairing fluctuations produces a strong specific signature in the current-voltage characteristics. Our results show that fluctuations survive only close to Tc (T-Tc<15K) and therefore cannot be responsible for the opening of the pseudogap at high temperature.