Effects of divalent impurities on the fluctuation conductivity of YBa2Cu3O7 single crystals

✍ Scribed by V.N. Vieira; F.T. Dias; P. Pureur; J. Schaf

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 213 KB
• Volume: 404
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/j.physb.2009.07.059

✦ Synopsis

In order to test the stability of the observed fluctuation regimes, low magnetic fields were applied perpendicular to the Cu-O 2 atomic planes. When the transition is approached from above we first observe a three-dimensional (3D) Gaussian regime then a crossover to a genuine critical region where the exponent is consistent with the predictions of the 3D-XY-E universality class. Decreasing further the temperature towards T c , our results systematically reveal the occurrence of a regime beyond 3D-XY characterized by a very small critical exponent. We propose that this regime is precursory to a weak first-order superconducting transition driven by antiferromagnetic excitations related to the pseudogap phenomenon. The dilution of divalent impurities in YBa 2 Cu 3 O 7 does not affect the stability of the fluctuation regime beyond 3D-XY and in the case of Ca doping a further approach towards the first-order behaviour is observed.