Moduli Instability in Warped Compactifications of the Type IIB Supergravity

We show that the conifold and deformed-conifold warped compactifications of the ten-dimensional type IIB supergravity, including the Klebanov-Strassler solution, are dynamically unstable in the moduli sector representing the scale of a Calabi-Yau space, although it can be practically stable for a quite long time in a region with a large warp factor. This instability is associated with complete supersymmetry breaking except for a special case and produces significant time-dependence in the structure of the four-dimensional base spacetime as well as of the internal space.Comment: 24 pages, no figure. Typos corrected, and some arguments in section 5 are adde

Novel Josephson Junction Geometries in NbCu bilayers fabricated by Focused Ion Beam Microscope

We explore novel junction configurations as an extension of our established Focused Ion Beam-based low TC SNS Junction fabrication technique. By milling a circular trench (diameter 1 micron, width 50 nm) in a 125 nm Nb 75 nm Cu bilayer we define a superconducting island connected to the bulk of the film by a normal metal barrier and entirely enclosed in-plane by the superconducting film. The circular junction properties can be probed by depositing an insulating layer over the device and drilling a 0.3 micron diameter hole down to the island to allow a Nb via to be deposited. Device behavior has been studied at 4.2 K. An SNS-like current voltage characteristic and Shapiro steps are observed. It is in terms of magnetic field behavior that the device exhibits novel characteristics: as the device is entirely enclosed in type II superconductor, when a magnetic field is applied perpendicular to the plane of the film, only quantized flux can enter the junction. Hence as applied magnetic field is increased the junction critical current is unchanged, then abruptly suppressed as soon as a flux quantum enters (close to the expected value of lower critical field for the film).Comment: 10 pages including 6 figures Minor Corrections inlight of referees' comment

Advances in single crystal growth and annealing treatment of electron-doped HTSC

High quality electron-doped HTSC single crystals of $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ have been successfully grown by the container-free traveling solvent floating zone technique. The optimally doped $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ crystals have transition temperatures $T_{\rm c}$ of $25$\,K and $23.5$\,K, respectively, with a transition width of less than $1$\,K. We found a strong dependence of the optimal growth parameters on the Ce content $x$. We discuss the optimization of the post-growth annealing treatment of the samples, the doping extension of the superconducting dome for both compounds as well as the role of excess oxygen. The absolute oxygen content of the as-grown crystals is determined from thermogravimetric experiments and is found to be $\ge 4.0$. This oxygen surplus is nearly completely removed by a post-growth annealing treatment. The reduction process is reversible as demonstrated by magnetization measurements. In as-grown samples the excess oxygen resides on the apical site O(3). This apical oxygen has nearly no doping effect, but rather influences the evolution of superconductivity by inducing additional disorder in the CuO$_{2}$ layers. The very high crystal quality of $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ is particularly manifest in magnetic quantum oscillations observed on several samples at different doping levels. They provide a unique opportunity of studying the Fermi surface and its dependence on the carrier concentration in the bulk of the crystals.Comment: 19 pages, 7 figures, submitted to Eur. Phys. J.

Vertical Confinement and Evolution of Reentrant Insulating Transition in the Fractional Quantum Hall Regime

We have observed an anomalous shift of the high field reentrant insulating phases in a two-dimensional electron system (2DES) tightly confined within a narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the high field insulating states centered around $\nu = 1/5$, the 2DES confined within an 80\AA-wide quantum well exhibits the transition at $\nu = 1/3$. Comparably large quantum lifetime of the 2DES in narrow well discounts the effect of disorder and points to confinement as the primary driving force behind the evolution of the reentrant transition.Comment: 5 pages, 4 figure

Anomalous Scaling of Structure Functions and Dynamic Constraints on Turbulence Simulations

The connection between anomalous scaling of structure functions (intermittency) and numerical methods for turbulence simulations is discussed. It is argued that the computational work for direct numerical simulations (DNS) of fully developed turbulence increases as $Re^{4}$, and not as $Re^{3}$ expected from Kolmogorov's theory, where $Re$ is a large-scale Reynolds number. Various relations for the moments of acceleration and velocity derivatives are derived. An infinite set of exact constraints on dynamically consistent subgrid models for Large Eddy Simulations (LES) is derived from the Navier-Stokes equations, and some problems of principle associated with existing LES models are highlighted.Comment: 18 page

Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap

Measurement of the π−\pi^- decay width of Λ5^5_\LambdaHe

We have precisely measured $\Lambda \to p\pi^-$ decay width of \5LHe and demonstrated significantly larger $\alpha$ -$\Lambda$ overlap than expected from the central repulsion $\alpha$-$\Lambda$ potential, which is derived from YNG \Lambda$-nucleon interaction.Comment: 4 pages, 3 figure

Proton asymmetry in non-mesonic weak decay of light hypernuclei

We have obtained the decay asymmetry parameters in non-mesonic weak decay of polarized Lambda-hypernuclei by measuring the proton asymmetry. The polarized Lambda-hypernuclei, 5_Lambda-He, 12_Lambda-C, and 11_Lambda-B, were produced in high statistics via the (pi^+,k^+) reaction at 1.05 GeV/c in the forward angles. Preliminary analysis shows that the decay asymmetry parameters are very small for these s-shell and p-shell hypernuclei.Comment: 4pages, 4figures, International Conference on Hypernuclear and Strange Particle Physics (HYP2003

pi^0 decay branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei

We precisely measured pi^0 branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei produced via (pi^+,k^+) reaction. Using these pi^0 branching ratios with the pi^- branching ratios and the lifetimes, we obtained the pi^0 decay widths and the non-mesonic weak decay widths at high statistics with the accuracy of ~5 % (stat) for both hypernuclei.Comment: 4pages, 4figures, International Conference on Hypernuclear and Strange Particle Physics (HYP2003