Superconducting Gap Anisotropy and Quasiparticle Interactions: A Doping Dependent Photoemission Study

Abstract

Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the $d$-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear $T$ contribution to the superfluid density. Furthermore, although consistent with $d$-wave symmetry, the gap with underdoping cannot be fit by the simple $\mathrm{cos}{k}_{x}\ensuremath{-}\mathrm{cos}{k}_{y}$ form, which suggests an increasing importance of long range interactions as the insulator is approached.