Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.8: Poster

Montag, 26. März 2007, 14:00–17:45, Poster A

The bulge in the basal plane of cuprate superconductors - evidence for 3a singlet hole pair formation — •Jürgen Röhler — Universität zu Köln, 50937 Köln, Germany

In the cuprate superconductors the variaton of the basal lattice parameters upon doping is expected to follow the ubiquitous 1-logm behavior of interatomic distances in systems with varying covalency – a behavior discovered by L. Pauling within his theory of resonant valence bonds. m is the degree of covalency. Detailed crystallographic work from the hole doped cuprates, however, finds the interatomic distances in the CuO₂ planes (plotted as a² or ab) concave away from the doping axis, not convex toward it. The resulting bulge in the basal plane area is maximum at optimum doping n_opt≃ 0.16, and collapses within the weakly overdoped regime around n≃ 0.22. We connect the bulge with a doping dependent repulsive interaction arising from the higher stability of the resonant (ZR) singlet hole states relative to that of single nn singlet hole states. Thus ZR singlet hole states tend to suppress double occupations of their oxygen cages, hence suppressing the formation of nonresonant 1a (nn) singlet hole pairs. Instead 3a singlet hole pairs comprising 4 oxygen cages are favored. Within the concept of a superconducting quantum liquid of valence bonds resonating around among different pairings of atoms the constraint to 3a hole pair formation creates a strongly textured liquid with nodes along (π, π) in reciprocal space. We show that in this textured liquid 3a singlet hole pairs may propagate dissipationless along the Cu–O directions in the background of antiferromagnetically correlated Cu spins.