Anomalous spectral weight transfer at the superconducting transition of single-crystalline Bi2Sr2CaCu208+5 was observed by high-resolution angle-resolved photoemission spectroscopy. As the sample goes superconducting, not only is there spectral weight transfer from the gap region to the pileup peak as in BCS theory, but along the T-M direction there is also some spectral weight transfer from higher binding energies in the form of a dip. In addition, we note that at the superconducting transition there is a decrease (increase) in the occupied spectral weight for the spectra taken along T-M (T-X).PACS numbers: 74.65.+n, 71.20.Cf, 79.60.Cn In the BCS theory for traditional superconductors the electron Fermi sea is unstable to attractive interactions mediated by phonons. A superconducting gap is formed when the near-Fermi-edge electrons condense to form pairs at low temperatures. As illustrated in the inset of Fig.

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We observe hexatic order in Abrikosov flux lattices in very clean crystals of the high-7Y superconductor Bi2.iSri.9Cao.9Cii208+tf, by in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent 776 ~0.06± 0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the lowtemperature ordered phase of the flux lines in these systems might be a hexatic glass.

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