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

Abstract

Comparing ARPES 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 non-interacting 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 coskx-cosky form, which suggests an increasing importance of long range interactions as the insulator is approached.

The resonant magnetic mode: A common feature of high-Tc superconductors

“…3) Er < 2∆max ∼ 70 meV ∼ 9kBTc, which has been deduced either by photoemission measurements in BSCCO [30] or by the position of the B1g mode in Raman scattering; the latter has been measured for all cuprates. This agrees with models which interpret the resonant mode as a magnetic collective mode of the d x 2 −y 2 -wave superconducting state below the electron-hole continuum.…”

“…The red full curve shows the doping dependence of the superconducting temperature times 5.3. The figure also shows twice the maximum SC gap as measured in BSCCO by ARPES [30].…”

“…A close inspection of the Fermi surface [28] shows that the quasi-particles which are connected by the (π, π) momentum (corresponding to the "hot spots") have the energy E k ≃ 0.9∆max at the Fermi level. The p-h continuum threshold would then be ωc ≃ 1.8∆max ≃ 63 meV ( where the SC gap measured at optimal doping is ∆max= 35 meV [30]). The resonance peak is observed at optimal doping at an energy around 43 meV, clearly lower than ωc.…”

Gap and pseudogap evolution within the charge-ordering scenario for superconducting cuprates

“…Angle-resolved photoemission spectroscopy (ARPES) experiments indicate that the pseudogap and the superconducting gap have the same momentum dependence across T c , which almost resembles a d x 2 −y 2 -wave, Penetration depth measurements of the superfluid density ρ s (T ) at low temperature probe the low-energy excitations around the nodal points in a d-wave superconductor, and therefore ∆ 0 (π/4). The correspondence between ARPES measurements of ∆ 0 (π/4) and the slope of ρ s (T ) at T = 0 is made however more involved by the presence of the Landau renormalization factors [4].…”

Tc and deltao in a phenomenological ''pseudogap'' model

“…This is not a crazy idea, because it has been shown that the observed symmetry of the order parameter cannot be fitted with only the lowest harmonics of the d-wave order parameter [18,19,20,21]. Furthermore, a recent experiment with twisted Josephson junctions in the Bi-cuprates [22], is in favor of an extended s-wave order parameter, and has shown the absence of a dwave part in the order parameter.…”