Electrical resistance under pressure in textured Bi2Sr2CaCu2O8+y: Enhancement of the energy gap and thermodynamic fluctuations

The effects of hydrostatic pressure up to 1 GPa on the ab-plane electrical resistance of textured Bi2SrCaCu2O8+y have been measured. Use of the Ambegaokar-Halperin (AH) model to examine the pressure effects on weak links across grain boundary leads to a value of 0.12+/-0.02 GPa(-1) for the pressure derivative d[1n Delta(j)(0)]/dP of the energy gap Delta(j)(0) at junctions formed by grains; Delta(j)(0) for Bi2Sr2CaCu2O8+y is about 10 times smaller than that of YBa2Cu3O7-delta. The thermodynamic fluctuations of the superconducting order parameter have a two-dimensional character above T-c and below 115 K. Applying hydrostatic pressure enhances the thermodynamic fluctuations: creation of the superconducting quasiparticles well above T-c is enhanced under pressure. As pressure is increased, the characteristic thickness d of the two-dimensional system decreases nonlinearly by about 20% up to 0.71 GPa. The pressure derivatives dT(c)/dP of the superconducting transition temperature T-c have been determined as 1.6+/-0.3 KGPa(-1), 1.8+/-0.2 KGPa(-1), and 3.0+/-0.2 KGPa(-1) at the onset, midpoint, and offset of the R-T curve, respectively. Thermodynamic fluctuations affect dT(c)/dP at onset. The large value of dT(c)/dP at offset is due to the influence of the weak links at grain boundaries. A value of -1.4 is obtained for d 1nT(c)/d 1nV, which, like that for monocrystalline Bi-2.2(Sr,Ca)(2.8)Cu2O8+y, falls between those predicted by the BCS and the resonating valence-bond theories. In the normal state d 1n rho(ab)/dP is -8.4%+/-0.2 GPa(-1) at 293 K and d 1nR(ab)/d 1nV is 2.01+/-0.06. The pressure derivative d 1nR(ab)/dP of the normal-state resistance of textured Bi2Sr2CaCu2O8+y shows a temperature dependence, which is affected by applied pressure and thermodynamic fluctuations.