Possible weakly first-order superconducting transition induced by magnetic excitations in the YBCO system: A fluctuation conductivity study

• Published in: Physics letters. A 2017-04, Vol.381 (14), p.1255-1260
• Main Authors: Hneda, Marlon Luiz, da Silva Berchon, Luciano, Pureur, Paulo, das Neves Vieira, Valdemar, Jaeckel, Sandra Teixeira, Dias, Fábio Teixeira, Menegotto Costa, Rosângela
• Format: Article
• Language: English
• Subjects: Critical phenomena; Effects of impurities; Electrical resistivity; Fluctuation effect; Superconductivity; Y-based cuprates
• ISSN: 0375-9601; 1873-2429
• DOI: 10.1016/j.physleta.2017.02.001

Fluctuation conductivity is experimentally studied in the genuine critical region near the superconducting transition of YBa2Cu3O7−δ, YBa2Cu2.985Fe0.015O7−δ and Y0.95Ca0.05Ba2Cu3O7−δ single crystal samples. Two fluctuation regimes where the electrical conductivity diverges as a power-law of the reduced temperature were systematically observed. In the first regime, farther from the critical temperature Tc, the transition behaves as predicted by the thermodynamics of the three dimensional-XY (3D-XY) universality class characteristic of a second-order phase transition. In the asymptotic regime closer to Tc a power-law regime characterized by a much smaller exponent is observed. The smallest value ever reported for the fluctuation conductivity exponent in the high-Tc superconductors is obtained for the Fe- and Ca-doped systems. We suggest that the regime beyond 3D-XY is a crossover towards a weakly first-order transition induced by internal magnetic excitations. •It is obtained the smallest value reported for fluctuation conductivity exponent in HSTC.•The supercritical regime is interpreted as a precursor to a weak first order SC transition.•Slightly doping YBCO with Fe or Ca improves the stability of supercritical fluctuations.•The weak first order in YBCO is related to internal magnetic excitations.