Superconducting fluctuations, pseudogap and phase diagram in cuprates

¹ Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris Sud - 91405 Orsay, France, EU
² Service de Physique de l'Etat Condensé, Orme des Merisiers, CEA Saclay (CNRS URA 2464) 91191 Gif-sur-Yvette cedex, France, EU
³ Laboratoire des Champs Magnétiques Intenses, UPR 3228, CNRS-UJF-UPS-INSA - 31400 Toulouse, France, EU

^a alloul@lps.u-psud.fr

Received: 14 June 2010
Accepted: 23 July 2010

Abstract

We report transport measurements using pulsed magnetic fields to suppress the superconducting fluctuations (SCF) conductivity in a series of YBa₂Cu₃O_6+x samples. These experiments allow us altogether to measure the temperature T_c′ at which SCF disappear, and the pseudogap temperature T^*. While the latter are consistent with previous determinations of T^*, we find that T_c′ is slightly larger than similar data taken by Nernst measurements. A careful investigation near optimal doping shows that T^* becomes smaller than T_c′, which is an unambiguous evidence that the pseudogap cannot be assigned to preformed pairs. Studies of the incidence of disorder on both T_c′ and T^* allow us to propose a phase diagram including disorder which explains most observations done in other cuprate families, and to discuss the available knowledge on the pseudogap line in the phase diagram.