Quasi-particles in the pseudogap state

What is the relationship between the pseudogap and the superconducting in the underdoped cuprates?

A really nice ARPES (Angle-Resolved PhotoEmission) study by Shi et al. shows that in an underdoped LSCO (Tc=30K) they are one and the same.
The figure at right shows the supeconducting gap Delta (filled blue dots) at T=12 K as a function of phi=angle around the Fermi surface. phi=45 degrees is the node.
The open green circles are at T=49 K, i.e., well above Tc and into the pseudogap state.
Gamma1 is the electron lifetime as a function of angle at 12 K.

This is all consistent with perfect particle-hole symmetry and the quasi-particles in the pseudogap state being like Bogoliubov quasiparticles.

This follows an earlier paper by Norman et al. who compared ARPES spectra to that predicted by the one-electron Greens function from six alternative theories for the pseudogap state (D-density wave, nesting density wave, differing Luttinger surface, energy displaced node,...) The only one consistent with experiment is a d-wave superconducting fluctuation model provided one has different lifetimes in the particle-hole and particle-particle channels.

As an aside, I note this shows the value of the method of alternative hypotheses.