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Session Q10 - HTSC: THEORY OF OBSERVATION OF ORDER PRAMETER SYMETRY
Mixed session, Friday morning, March 24, 8:00
Ballroom A4, San Jose Convention Center
We theoretically study the symmetry of the superconducting gap in bilayer cuprates, such as YBCO, in the context of spin fluctuation theories. We explore the relative stability of d-wave symmetry which arises from strong intra-layer exchange of antiferromagnetic fluctuations, and a competing state with two opposite sign s-wave gaps. The latter derives from c-axis magnetic correlations which are observed in YBCO at all stoichiometries. Here, the two s gaps, which correspond to each of the two bands, have different magnitude and the same T_c . To establish the boundaries between s and d states, we explore the role of detailed bandstructure, orthorhombicity, Coulomb effects and electron phonon interactions. Depending on these parameters, the bilayer s-state is frequently the more stable and leads to interesting anisotropies in Josephson tunneling and superconducting electrodynamics, as well as impurity effects on T_c .