Observation of temperature-dependent site disorder inYBa2Cu3

Relaxation effects in the transition temperature of superconductingHgBa2CuO4+δ

“…The difference of 70 mK between the value of T c at the outset of the experiment (47.81 K) and the final value (47.74 K) is likely due to the different annealing temperature (here T a = 265 K versus 298 K for the initial measurement). We previously observed a similar effect in YBa 2 Cu 3 O 6.41 [14,31]. As we discuss in more detail below, a lower annealing temperature leads to a higher state of oxygen order which increases the hole-carrier concentration in the CuO 2 planes, shifting T c up for an underdoped sample or down for an overdoped sample, as observed.…”

“…T c (P) is thus not a unique function of pressure but depends strongly on the detailed temperaturepressure history of the sample. Because this anomalous behavior is a sensitive function of the concentration of interstitial oxygen δ in Tl-2201, it has been attributed [13] to relaxation effects within the oxygen sublattice; indeed, evidence for strong relaxation effects in T c from oxygen ordering were first obtained by Veal et al [14] in temperature-quench experiments on strongly underdoped YBa 2 Cu 3 O 7−y (Y-123). Evidence for relaxation effects in Y-123 from high-pressure data was obtained somewhat later [15,16].…”

High Pressure Effects on Superconductivity

“…12 and the enhancement of dT c /dp for room temperature pressure application is very obvious. This enhancement was attributed to the pressure-induced ordering of the chain oxygen in analogy to the results of the annealing experiments of Veal et al [83]. The pressure-induced redistribution of oxygen was investigated in more detail with respect to the characteristic time relaxation of T c at different temperatures [91,92].…”

“…From the pressure dependence of E A the activation volume for diffusion could be calculated and was found to be close to the molar volume of O 2- [93,95]. The observed changes of T c in YBCO with the re-distribution of the chain oxygen was explained by a charge transfer to the active CuO 2 layers that depends sensitively on the specific oxygen configuration [83,84]. This charge transfer also affects the electrical transport properties in the normal state.…”

Preparation and characterization of homogeneous YBCO single crystals with doping level near the SC-AFM boundary

“…The result is reversible and reproducible; that is, the saturation T c depends only on the final annealing temperature, independent of whether the crystals had been previously annealed at a higher or lower temperature. This indicates that the ordering is thermodynamically stable, and the dependence of T c on annealing temperature likely results from the temperature dependence of the average length of chain fragments [14,15,20].…”