The interlayer phase coherence in Bi 2 Sr 2 CaCu 2 O 81y was quantitatively determined in a wide field range by using the Josephson plasma resonance (JPR). At the first-order transition (FOT), a novel frequency-independent JPR with sharp resonance width is found, indicating a jump in the interlayer phase coherence. Above the FOT, sample-moving magnetization measurements show an anomaly consistent with the report by Fuchs et al. [Phys. Rev. Lett. 80, 4971 (1998)], where the interlayer phase coherence shows no anomaly. These results suggest the decoupling nature of the FOT, and can rule out the existence of the vortex line liquid state.

The magnetic penetration depth λ(T, H, j) was measured in the presence of a slowly relaxing supercurrent, j. In single crystal Bi2Sr2CaCu2O8 below approximately 25 K, λ(T, H, j) is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as j changes. The Campbell length depends upon the ratio j/jc where jc is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor.

Tunneling and theoretical studies have suggested that Andreev bound states form at certain surfaces of unconventional superconductors. Through studies of the temperature and field dependence of the in-plane magnetic penetration depth λ ab at low temperature, we have found strong evidence for the presence of these states in clean single crystal YBCO and BSCCO. Crystals cut to expose a [110] interface show a strong upturn in λ ab at around 7 K, when the field is oriented so that the supercurrents flow around this surface. In YBCO this upturn is completely suppressed by a field of ∼ 0.1 T.PACS numbers: 74.25.NfThe low temperature behavior of the magnetic penetration depth (λ) has played an important role in identifying the bulk order parameter in the high T c cuprates. Within the usual BCS quasiparticle picture, the temperature and field dependence of λ are determined by the energy dependence of the quasiparticle density of states N (E), and hence give information about the magnitude of the energy gap, but not its phase. Recently however, it has been suggested that there is another contribution to λ which arises from current carrying, zero energy, surface Andreev bound states (ABS) [1], which form if there is π phase shift between the different lobes of the order parameter [2][3][4]. The observation of these states provides a key piece of evidence backing the d-wave scenario in the cuprates. In addition, this extra contribution has important consequences for the interpretation of all surface impedance measurements in non-conventional superconductors.The zero bias conductance peak (ZBCP) observed in tunneling measurements has been interpreted as resulting from ABS [5,2] . This has been interpreted as resulting from surface roughness and/or nanofaceting [2]. The contribution of the ABS to λ can be understood simply by noting the increase in the penetration depth ∆λ due to thermally excited quasiparticles is given bywhere f is the Fermi function. For a d-wave superconductor N (E) ∼ |E|, which gives ∆λ(T )/λ(0) = αT , where α depends on the angular slope of the energy gap near the nodes [6]. Surface bound states add a singular contribution δ(E) to N (E) which when substituted into Eq. (1) adds a divergent 1/T term to ∆λ(T ). The relative size of 1/T term depends on the orientation of the surface and the band structure of the material [4]. The ABS contribution to λ is highly non-linear in field, as the superflow Doppler shifts of the position of the bound state peaks. It is therefore expected that the 1/T term is suppressed with a relatively weak magnetic field. In this letter, we report measurements of the temperature and field dependence of the in-plane penetration depth of high quality YBa 2 Cu 3 O 6.9 and Bi 2 Sr 2 CaCu 2 O 8 single crystals which provide strong evidence of the existence of ABS in these materials. Evidence for an ABS contribution to λ have previously been identified from studies of irradiated thin films [3] and grain boundary junctions [7]. Here, we have been able to investigate the ABS more fully ...

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We have grown SiO 2 films on polycrystalline Si using excited ozone produced by ultraviolet light irradiation of ozone, and characterized their electrical properties in the metal-insulator-semiconductor capacitor configuration. SiO 2 films of ϳ8.5 nm thickness on poly-Si layers were grown in 60 min even at room temperature. The leakage current density across the SiO 2 film fitted well the Fowler-Nordheim tunnel current behavior and breakdown occurred at above 12 MV/cm, showing that the film was of device quality. The rate of Si oxidation by excited ozone was similar for both Si͑100͒ and Si͑111͒ wafers, as was the interface trap density ͑D it ͒. These results indicate that excited ozone can form a homogenous SiO 2 film on poly-silicon. We conclude that excited ozone is one of the most efficient reactive species for SiO 2 film formation on poly-Si at room temperature.