4,676 research outputs found

    Spatially Resolved NMR Relaxation Rate in a Noncentrosymmetric Superconductor

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    We numerically study the spatially-resolved NMR around a single vortex in a noncentrosymmetric superconductor such as CePt3Si. The nuclear spin-lattice relaxation rate 1/T1 under the influence of the vortex core states is calculated for an s+p-wave Cooper pairing state. The result is compared with that for an s-wave pairing state.Comment: 2 pages; submitted to Proc. of SCES'0

    Nuclear Magnetic Relaxation Rate in the Vortex State of a Chiral p-Wave Superconductor

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    The site-selective nuclear spin-lattice relaxation rate T1^{-1} is theoretically studied inside a vortex core in a chiral p-wave superconductor within the framework of the quasiclassical theory of superconductivity. It is found that T1^{-1} at the vortex center depends on the sense of the chirality relative to the sense of the magnetic field. Our numerical result shows a characteristic difference in T1^{-1} between the two chiral states, k_x + i k_y and k_x - i k_y under the magnetic field.Comment: 2 pages, 2 figures; To be published in Physica C; Proc. of LT23, Hiroshima (Japan), 20-27 Aug. 200

    Effects of mass renormalization on the surface properties of heavy-ion fusion potential

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    We discuss the effects of fast nuclear excitations on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Using the fusion of two 40^{40}Ca nuclei as an example and the inversion method, we show that the mass renormalization induced by fast nuclear excitations leads to a large surface diffuseness in the effective potential for heavy-ion fusion reactions.Comment: 13 pages, Late

    Sparse Learning over Infinite Subgraph Features

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    We present a supervised-learning algorithm from graph data (a set of graphs) for arbitrary twice-differentiable loss functions and sparse linear models over all possible subgraph features. To date, it has been shown that under all possible subgraph features, several types of sparse learning, such as Adaboost, LPBoost, LARS/LASSO, and sparse PLS regression, can be performed. Particularly emphasis is placed on simultaneous learning of relevant features from an infinite set of candidates. We first generalize techniques used in all these preceding studies to derive an unifying bounding technique for arbitrary separable functions. We then carefully use this bounding to make block coordinate gradient descent feasible over infinite subgraph features, resulting in a fast converging algorithm that can solve a wider class of sparse learning problems over graph data. We also empirically study the differences from the existing approaches in convergence property, selected subgraph features, and search-space sizes. We further discuss several unnoticed issues in sparse learning over all possible subgraph features.Comment: 42 pages, 24 figures, 4 table

    Electronic structure and spontaneous internal field around non-magnetic impurities in spin-triplet chiral p-wave superconductors

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    The electronic structure around an impurity in spin triplet p-wave superconductors is studied by the Bogoliubov-de Gennes theory on a tight-binding model, where we have chosen sinpx+isinpy\sin{p_x}{+}{\rm i}\sin{p_y}-wave or sin(px+py)+isin(px+py)\sin{(p_x+p_y)}{+}{\rm i}\sin{({-}p_x{+}p_y)}-wave states which are considered to be candidates for the pairing state in Sr2_{2}RuO4_{4}. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between the two types of pairing. We propose that it is possible to discriminate the two pairing states by studying the spatial dependence of the magnetic field around a pair of impurities.Comment: 4 pages, 4 figure

    A two-channel Kondo impurity in the spin-1/2 chain: Consequences for Knight shift experiments

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    A magnetic impurity in the spin-1/2 chain is a simple realization of the two-channel Kondo problem since the field theoretical descriptions in the spin-sector are identical. The correlation functions near the impurity can be calculated. Using a modified version of the numerical transfer matrix DMRG, we are able to accurately determine local properties close to the impurity in the thermodynamic limit. The local susceptibilities (Knight-shifts) show an interesting behavior in a large range around the impurities. We are able to make quantitative experimental predictions which would allow to observe two-channel Kondo physics for the first time directly by doping of spin-1/2 chain compounds.Comment: 2 pages in revtex format including 2 embedded figures (using epsf

    Iterative Deconvolution of Quadrupole Split NMR Spectra

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    We propose a simple method to deconvolute NMR spectra of quadrupolar nuclei in order to separate the distribution of local magnetic hyperfine field from the quadrupole splitting. It is based on an iterative procedure which allows to express the intensity of a single NMR line directly as a linear combination of the intensities of the total experimental spectrum at a few related frequencies. This procedure is argued to be an interesting complement to Fourier transformation since it can lead to a significant noise reduction in some frequency ranges. This is demonstrated in the case of the 11B-NMR spectrum in SrCu2(BO3)2 at a field of 31.7 T, where a magnetization plateau at 1/6 of the saturation has been observed.Comment: 4 pages, 2 figure
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