https://doi.org/10.1007/s100510050858
"W = 0" pairing in Cu-O clusters and in the plane
INFM, Dipartimento di Fisica,
Università di Roma Tor Vergata, Via
della Ricerca Scientifica 1, 00133 Roma, Italy
Corresponding author: a cini@roma2.infn.it
Received:
18
December
1998
Published online: 15 July 1999
The Cu-O plane and the clusters that possess the same symmetry around a Cu
ion have 2-hole eigenstates of the kinetic energy with vanishing on-site repulsion
(W=0 pairs).
Cluster calculations by exact diagonalisation show that these are the quasiparticles
that lead to a paired ground state, and have superconducting flux-quantisation
properties. Here, we extend the theory to the full plane, and show that the W=0
quasiparticles are again the natural explanation of superconducting flux-quantisation.
Moreover, by a new approach which is exact in principle, we calculate the effective
interaction Weff between two holes added to the ground state of the repulsive
three-band Hubbard model. To explain how a noninteracting electron gas becomes a
superconductor when switching the local Coulomb interaction, we obtain a closed-form
analytic expression including the effects of all virtual transitions to 4-body
intermediate states (exchange of an electron-hole pair).
Our scheme is ready to include other interactions which are not considered
in the Hubbard model but may be important. In the plane, the W=0 pairs have
and
symmetry. The effective interaction in these
channels is attractive and leads to a Cooper-like instability of the Fermi
liquid, while it is repulsive for triplet pairs. From Weff, we derive an
integral equation for the pair eigenfunction; the binding energy
of the pairs is in the range of tens of meV. However, our
symmetry-based method is far more general than the model.
PACS: 74.20.Mn – Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.) / 71.10.Li – Excited states and pairing interactions in model systems
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999