Enhancement of pseudogap anomalies induced by nanoscale structural inhomogeneity in YBa₂Cu₃O_6.93 high-<em class="EmphasisTypeItalic ">T</em> _c superconductor

The magnetization <em class="EmphasisTypeItalic ">M</em>(<em class="EmphasisTypeItalic ">H</em>) in the superconducting state, dc magnetic susceptibility χ(<em class="EmphasisTypeItalic ">T</em>) in the normal state, and specific heat <em class="EmphasisTypeItalic ">C</em>(<em class="EmphasisTypeItalic ">T</em>) near the superconducting transition temperature <em class="EmphasisTypeItalic ">T</em> _c have been measured for a series of fine-crystalline YBa₂Cu₃O_{<em class="EmphasisTypeItalic ">y</em>} samples having nearly optimum values of <em class="EmphasisTypeItalic ">y</em> = 6.93 ± 0.3 and <em class="EmphasisTypeItalic ">T</em> _c = (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 <em class="EmphasisTypeItalic ">H</em> _c are determined by the analysis of the magnetization curves <em class="EmphasisTypeItalic ">M</em>(<em class="EmphasisTypeItalic ">H</em>). 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 <em class="EmphasisTypeItalic ">H</em> _c(<em class="EmphasisTypeItalic ">T</em>) and the jump of the specific heat Δ<em class="EmphasisTypeItalic ">C</em>/<em class="EmphasisTypeItalic ">T</em> _c. 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(<em class="EmphasisTypeItalic ">T</em>). It is found that the nanoscale structural inhomogeneity significantly enhances and probably even creates the pseudogap regime in the optimally doped high-<em class="EmphasisTypeItalic ">T</em> _c superconductors.