Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+d

Abstract

Pairing of electrons in conventional superconductors occurs at the superconducting transition temperature Tc, creating an energy gap D in the electronic density of states (DOS). In the high-Tc superconductors, a partial gap in the DOS exists for a range of temperatures above Tc. A key question is whether the gap in the DOS above Tc is associated with pairing, and what determines the temperature at which incoherent pairs form. Here we report the first spatially resolved measurements of gap formation in a high-Tc superconductor, measured on Bi2Sr2CaCu2O8+d samples with different Tc values (hole concentration of 0.12 to 0.22) using scanning tunnelling microscopy. Over a wide range of doping from 0.16 to 0.22 we find that pairing gaps nucleate in nanoscale regions above Tc. These regions proliferate as the temperature is lowered, resulting in a spatial distribution of gap sizes in the superconducting state. Despite the inhomogeneity, we find that every pairing gap develops locally at a temperature Tp, following the relation 2D/kBTp = 8. At very low doping (<0.14), systematic changes in the DOS indicate the presence of another phenomenon, which is unrelated and perhaps competes with electron pairing. Our observation of nanometre-sized pairing regions provides the missing microscopic basis for understanding recent reports of fluctuating superconducting response above Tc in hole-doped high-Tc copper oxide superconductors.

References in corpus (2)

• A `checkerboard' electronic crystal state in lightly hole-doped Ca_{2-x}Na_{x}CuO_{2}Cl_{2}
• The Ground State of the Pseudogap in Cuprate Superconductors

Cited by in corpus (11)

• Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+d
• Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}
• Nodal/Antinodal Dichotomy and the Two Gaps of a Superconducting Doped Mott Insulator
• Influence of the pair coherence on the charge tunneling through a quantum dot connected to a superconducting lead
• Doping dependence of the vortex-core energy in bilayer films of cuprates
• Fermi Arcs in the Superconducting Clustered State for Underdoped Cuprates
• Doping Dependence of Two Energy Scales in the Tunneling Spectra of Superconducting La${}_{2-x}$Sr${}_x$CuO${}_4$
• Understanding the Protected Nodes and Collapse of the Fermi Arcs in Underdoped Cuprate Superconductors
• $T_c$ Dependence of Energy Gap and Asymmetry of Coherence Peaks in NdBa${}_2$Cu${}_3$O${}_{7-\delta }$
• Temperature and Spatial Dependence of the Superconducting and Pseudogap of NdFeAsO0.86F0.14
• Abrupt Onset of Second Energy Gap at Superconducting Transition of Underdoped Bi2212