Superconducting condensate residing on small Fermi pockets in underdoped cuprates

Abstract

How does Fermi surface develop upon doping of cuprates, does it consist of large barrels or small pockets, which of them is responsible for superconductivity, and what is a role of the pseudogap? Those are actively debated questions, important for understanding of high temperature superconductivity. We study doping dependence of intrinsic tunneling in Bi2Sr2Ca1−xYxCu2O8+δ cuprates, which allows independent analysis of Cooper pair and quasiparticle transport. We observe that with decreasing doping the supercurrent is rapidly decreasing at a rate much faster than the doping level, but the quasiparticle resistance at a sufficiently high bias remains almost doping independent. This remarkable discrepancy indicates that Cooper pairs and quasiparticles are originating from different parts of the Brillouin zone: Cooper pairs are residing on small pockets, which are progressively shrinking with decreasing doping, but the majority of the quasiparticle current is integrated over large barrels, which are only weakly doping dependent. The expanding pseudogap areas along the barrels do not contribute to pair current. This provides direct evidence for nonsuperconducting origin of the pseudogap. We present numerical calculations, taking into account Fermi surface topology, that support our conclusions.

Source-reported materials — not catalogue approval

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