Evidence for k-dependent, in-plane anisotropy of the superconducting gap in Bi2Sr2CaCu2O8+δ

Abstract

We find the superconducting gap in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystals is anisotropic in k space by roughly a factor of 2 using angle-resolved photoemission spectroscopy. Matching the k-space symmetry of the gap values provides a stringent constraint on theories of the mechanism of high-temperature superconductivity. A review of the literature shows that many puzzling results can be explained by anisotropic gaps in the high-${\mathit{T}}_{\mathit{c}}$ cuprates.