75,511 research outputs found

    Quantum interference in nested d-wave superconductors: a real-space perspective

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    We study the local density of states around potential scatterers in d-wave superconductors, and show that quantum interference between impurity states is not negligible for experimentally relevant impurity concentrations. The two impurity model is used as a paradigm to understand these effects analytically and in interpreting numerical solutions of the Bogoliubov-de Gennes equations on fully disordered systems. We focus primarily on the globally particle-hole symmetric model which has been the subject of considerable controversy, and give evidence that a zero-energy delta function exists in the DOS. The anomalous spectral weight at zero energy is seen to arise from resonant impurity states belonging to a particular sublattice, exactly as in the 2-impurity version of this model. We discuss the implications of these findings for realistic models of the cuprates.Comment: 12 pages, 10 figs, submitted to Phys. Rev.

    Two impurities in a d-wave superconductor:local density of states

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    We study the problem of two local potential scatterers in a d-wave superconductor, and show how quasiparticle bound state wave functions interfere. Each single-impurity electron and hole resonance energy is in general split in the presence of a second impurity into two, corresponding to one even parity and one odd parity state. We calculate the local density of states (LDOS), and argue that scanning tunneling microscopy (STM) measurements should be capable of extracting information about the Green's function in the pure system by a systematic study of 2-impurity configurations. In some configurations highly localized, long-lived states are predicted. We discuss the effects of realistic band structures, and how 2-impurity STM measurements could help distinguish between current explanations of LDOS impurity spectra in the BSCCO-2212 system.Comment: 16 pages,21 figure,New Version to be Published on P.R.

    Coarse-Grained Picture for Controlling Complex Quantum Systems

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    We propose a coarse-grained picture to control ``complex'' quantum dynamics, i.e., multi-level-multi-level transition with a random interaction. Assuming that optimally controlled dynamics can be described as a Rabi-like oscillation between an initial and final state, we derive an analytic optimal field as a solution to optimal control theory. For random matrix systems, we numerically confirm that the analytic optimal field steers an initial state to a target state which both contains many eigenstates.Comment: jpsj2.cls, 2 pages, 3 figure files; appear in J. Phys. Soc. Jpn. Vol.73, No.11 (Nov. 15, 2004

    Numerical simulations of negative-index refraction in wedge-shaped metamaterials

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    A wedge-shaped structure made of split-ring resonators (SRR) and wires is numerically simulated to evaluate its refraction behavior. Four frequency bands, namely, the stop band, left-handed band, ultralow-index band, and positive-index band, are distinguished according to the refracted field distributions. Negative phase velocity inside the wedge is demonstrated in the left-handed band and the Snell's law is conformed in terms of its refraction behaviors in different frequency bands. Our results confirmed that negative index of refraction indeed exists in such a composite metamaterial and also provided a convincing support to the results of previous Snell's law experiments.Comment: 18 pages, 6 figure

    Electromagnetic decays of vector mesons as derived from QCD sum rules

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    We apply the method of QCD sum rules in the presence of external electromagnetic fields FμνF_{\mu\nu} to the problem of the electromagnetic decays of various vector mesons, such as ρπγ\rho\to\pi\gamma, KKγK^\ast\to K\gamma and ηργ\eta'\to\rho\gamma. The induced condensates obtained previously from the study of baryon magnetic moments are adopted, thereby ensuring the parameter-free nature of the present calculation. Further consistency is reinforced by invoking various QCD sum rules for the meson masses. The numerical results on the various radiative decays agree very well with the experimental data.Comment: To appear in Phys. Lett.

    Magnetic Moments of JP=3/2+J^P={3/2}^+ Pentaquarks

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    If the JPJ^P of Θ5+\Theta_5^+ and Ξ5\Xi_5^{--} pentaquarks is really found to be 12+{1\over 2}^+ by future experiments, they will be accompanied by JP=32+J^P={3\over 2}^+ partners in some models. It is reasonable to expect that these JP=32+J^P={3\over 2}^+ states will also be discovered in the near future with the current intensive experimental and theoretical efforts. We estimate JP=3/2+J^P={3/2}^+ pentaquark magnetic moments using different models.Comment: 13 page
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