Increase of superfluid density with growth of quasiparticle density of states probed by intrinsic tunneling spectroscopy in Bi_(1.9)Pb_(0.1)Sr_2CaCu_2O_(8+δ)

摘要

Interlayer tunneling spectra, the Josephson critical current density J_c, and the normal tunneling resistance have been measured simultaneously for intrinsic Josephson junctions of Bi_(1.9)Pb_(0.1)Sr_2CaCu_2O_(8+δ) (BiPb2212) in the underdoped region using a small mesa structure (S=1×1 μm~2) and a short-pulse technique. J_c was significantly enhanced when Bi was partially replaced with Pb. By comparing J_c with the value estimated by the Ambegaokar-Baratoff formula, it was found that superfluid density doubles in the Pb-containing sample. In addition, Pb raises the superconducting coherence peak without changing the value of the superconducting gap A. Based on a model that accounts for the inhomogeneity of A in k space, we argue that the superfluid density increases because Pb substitution increases the homogeneity of Δ(k).