Je. Hirsch, Superconductivity from undressing. II. Single-particle Green's function and photoemission in cuprates, PHYS REV B, 62(21), 2000, pp. 14498-14510
Experimental evidence indicates that the superconducting transition in high
-T-c cuprates is an "undressing" transition. Microscopic mechanisms giving
rise to this physics were discussed in the first paper of this series. Here
we discuss the calculation of the single-particle Green's function and spe
ctral function for Hamiltonians describing undressing transitions in the no
rmal and superconducting states. A single parameter Y describes the strengt
h of the undressing process, and drives the transition to superconductivity
. In the normal state, the spectral function evolves from predominantly inc
oherent to partly coherent as the hole concentration increases. In the supe
rconducting state, the "normal" Green's function acquires a contribution fr
om the anomalous Green's function when Y is nonzero; the resulting contribu
tion to the spectral function is positive for hole extraction, and negative
for hole injection. It is proposed that these results explain the observat
ion of sharp quasiparticle states in the superconducting state of cuprates
along the (pi ,0) direction, and their absence along the (pi,pi) direction.