Enhancement of pseudogap anomalies induced by nanoscale structural inhomogeneity in YBa2Cu3O6.93 high-T c superconductor

Abstract

The magnetization M(H) in the superconducting state, dc magnetic susceptibility χ(T) in the normal state, and specific heat C(T) near the superconducting transition temperature Tc have been measured for a series of fine-crystalline YBa2Cu3Oy samples having nearly optimum values of y = 6.93 ± 0.3 and Tc = (91.5 ± 0.5) K. The samples differ only in the degree of nanoscale structural inhomogeneity. The characteristic parameters of superconductors (the London penetration depth and the Ginzburg–Landau parameter) and the thermodynamic critical field Hc are determined by the analysis of the magnetization curves M(H). It is found that the increase in the degree of nanoscale structural inhomogeneity leads to an increase in the characteristic parameters of superconductors and a decrease in Hc(T) and the jump of the specific heat ΔC/Tc. It is shown that the changes in the physical characteristics are caused by the suppression of the density of states near the Fermi level. The pseudogap is estimated by analyzing χ(T). It is found that the nanoscale structural inhomogeneity significantly enhances and probably even creates the pseudogap regime in the optimally doped high-Tc superconductors.