Pairing fluctuation in the pseudogap phase of superconducting cuprates

The origin of the pseudogap phase and its relation with superconductivity in underdoped cuprates has been a matter of debate for the last twenty years. We proposed to probe the pairing fluctuations in a Josephson like experiment. For that we fabricated a juntion in which one layer is an underdoped superconductor above its Tc, while the other layer is an optimally doped superconductor well below its own Tc (underdoped YBaCuO/PrBaCuO/optimally doped YBaCuO). At low temperature, when both electrodes are in the superconducting state, a Josephson behavior is observed. In the intermediate regime, when one electrode is in the superconducting state and the other one in the pseudogap state, we observed a signature of pairing fluctuations in a temperature range of 15K above the transition temperature, which is much lower than the characteristic temperature of the pseudogap (250K). This result is in favor of a classical scenario where the pairing fluctuations are limited to the vicinity of the transition.

Main references :

Probing pairing fluctuations in the pseudogap state of cuprates by Josephson effect N. Bergeal, J. Lesueur, M. Aprili, G. Faini, B. Leridon and J-P. Contour
Nature Phys. 4, 608 - 611 (2008)

Using ion irradiation de make High-Tc Josephson junctions N. Bergeal, J. Lesueur, M. Sirena, M. Aprili, J-P. Contour and B. Leridon
J. Appl. Phys. 102, 083903 (2007).