Fluctuation-Induced Conductivity of Polycrystalline (Ho–Ce)Ba 2 Cu 3 O $_{7-\boldsymbol\delta}$ Superconductor

Abstract

We report on systematic conductivity fluctuation measurements on samples of Ho 1−x Ce x Ba 2 Cu 3 O 7−δ with x = 0.00, 0.05, and 0.10. The samples were produced by a standard solid-state reaction method, and the microstructure was analyzed by X-ray diffraction. To identify power-law divergences of the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity dρ/dT and with the logarithmic derivative of the conductivity with respect to temperature −d ln( σ )/dT. It was observed that the critical temperature decreases and that the transition width increases with increasing Ce doping. The data showed the occurrence of a two-stage transition besides the pairing transition splitting, associated with Ce doping and related with the occurrence of a phase separation. Above the critical temperature, the Gaussian and critical regimes were observed. On approaching the zero resistance state, our results showed a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array.

Splitting of the pairing transition and coherence transition in R1−xCexBa2Cu3O7−δ(R = Y, Er, Ho and Gd)

“…However, the main peak, denoted by T P1 , is less affected by cerium doping. The same behavior is also observed for other rare earths studied [14][15][16][17].…”

“…C in air for 24 h and then slowly cooled through 700 • C. Finally, all samples were heated in flowing oxygen at 400 • C for 48 h. Specifically for Gd 0.95 Ce 0.05 Ba 2 Cu 3 O 7−δ , samples were also produced by another thermal treatment to investigate its effect on the splitting of the pairing transition. Appropriate quantities of precursor powders were mixed, ground and heated at 850 and 880 • C in air for 24 h. Then, they were reground, pressed in pellets and sintered at 920 • C for 24 h. After, the pellets were slowly cooled to room temperature to be heat-treated in flowing oxygen at 400 • C for 48 h. Sample preparation was also described elsewhere [14][15][16][17]. The x-ray diffraction patterns for Er, Gd and Ho samples were obtained using a Shimadzu diffractometer with Cu Kα radiation in 0.02 • steps and in scan mode from 20 • to 120 • .…”