4,807 research outputs found

    Collapse arrest and soliton stabilization in nonlocal nonlinear media

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    We investigate the properties of localized waves in systems governed by nonlocal nonlinear Schrodinger type equations. We prove rigorously by bounding the Hamiltonian that nonlocality of the nonlinearity prevents collapse in, e.g., Bose-Einstein condensates and optical Kerr media in all physical dimensions. The nonlocal nonlinear response must be symmetric, but can be of completely arbitrary shape. We use variational techniques to find the soliton solutions and illustrate the stabilizing effect of nonlocality.Comment: 4 pages with 3 figure

    Nuclear spin-lattice relaxation rate in the D+iD superconducting state: implications for CoO superconductor

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    We calculated the nuclear spin-lattice relaxation rate 1/T11/T_1 for the D+iD superconducting state with impurities. We found that small amount of unitary impurities quickly produces the residual density of states inside the gap. As a result, the T-linear behavior in 1/T1_1 is observed at low temperatures. Our results show that the D+iD pairing symmetry of the superconducting state of Na0.35_{0.35}CoO2y_{2} \cdot yH2_2 O is compatible with recent 59^{59}Co 1/T1_1 experiments of several groups.Comment: 5 pages, 4 figures, minor change

    Are there nodes in LaFePO, BaFe2_2(AsP)2_2, and KFe2_2As2_2 ?

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    We reexamined the experimental evidences for the possible existence of the superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC compounds: LaFePO, BaFe2_2(As0.67_{0.67}P0.33_{0.33})2_2, and KFe2_2As2_2. We showed that while the TT-linear temperature dependence of the penetration depth λ(T)\lambda(T) of these three compounds indicate extremely clean nodal gap superconductors, the thermal conductivity data limT,H0κS(H,T)/T\lim_{T,H \rightarrow 0} \kappa_S (H,T)/T unambiguously showed that LaFePO and BaFe2_2(As0.67_{0.67}P0.33_{0.33})2_2 are extremely dirty, while KFe2_2As2_2 can be clean. This apparently conflicting experimental data casts a serious doubt on the nodal gap possibility on LaFePO and BaFe2_2(As0.67_{0.67}P0.33_{0.33})2_2.Comment: 11 pages, 5 figures A new section "4. Remark on the quantum oscillation (QO) experiments" is adde

    Dynamic Fano Resonance of Quasienergy Excitons in Superlattices

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    The dynamic Fano resonance (DFR) between discrete quasienergy excitons and sidebands of their ionization continua is predicted and investigated in dc- and ac-driven semiconductor superlattices. This DFR, well controlled by the ac field, delocalizes the excitons and opens an intrinsic decay channel in nonlinear four-wave mixing signals.Comment: 4pages, 4figure

    Regular quantum graphs

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    We introduce the concept of regular quantum graphs and construct connected quantum graphs with discrete symmetries. The method is based on a decomposition of the quantum propagator in terms of permutation matrices which control the way incoming and outgoing channels at vertex scattering processes are connected. Symmetry properties of the quantum graph as well as its spectral statistics depend on the particular choice of permutation matrices, also called connectivity matrices, and can now be easily controlled. The method may find applications in the study of quantum random walks networks and may also prove to be useful in analysing universality in spectral statistics.Comment: 12 pages, 3 figure

    Direct measurement of a pure spin current by a polarized light beam

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    The photon helicity may be mapped to a spin-1/2, whereby we put forward an intrinsic interaction between a polarized light beam as a ``photon spin current'' and a pure spin current in a semiconductor, which arises from the spin-orbit coupling in valence bands as a pure relativity effect without involving the Rashba or the Dresselhaus effect due to inversion asymmetries. The interaction leads to circular optical birefringence, which is similar to the Faraday rotation in magneto-optics but nevertheless involve no net magnetization. The birefringence effect provide a direct, non-demolition measurement of pure spin currents.Comment: Erratum version to [Physical Review Letter 100, 086603 (2008)

    Stability of two-dimensional spatial solitons in nonlocal nonlinear media

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    We discuss existence and stability of two-dimensional solitons in media with spatially nonlocal nonlinear response. We show that such systems, which include thermal nonlinearity and dipolar Bose Einstein condensates, may support a variety of stationary localized structures - including rotating spatial solitons. We also demonstrate that the stability of these structures critically depends on the spatial profile of the nonlocal response function.Comment: 8 pages, 9 figure

    Characteristics of the polymer transport in ratchet systems

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    Molecules with complex internal structure in time-dependent periodic potentials are studied by using short Rubinstein-Duke model polymers as an example. We extend our earlier work on transport in stochastically varying potentials to cover also deterministic potential switching mechanisms, energetic efficiency and non-uniform charge distributions. We also use currents in the non-equilibrium steady state to identify the dominating mechanisms that lead to polymer transportation and analyze the evolution of the macroscopic state (e.g., total and head-to-head lengths) of the polymers. Several numerical methods are used to solve the master equations and nonlinear optimization problems. The dominating transport mechanisms are found via graph optimization methods. The results show that small changes in the molecule structure and the environment variables can lead to large increases of the drift. The drift and the coherence can be amplified by using deterministic flashing potentials and customized polymer charge distributions. Identifying the dominating transport mechanism by graph analysis tools is found to give insight in how the molecule is transported by the ratchet effect.Comment: 35 pages, 17 figures, to appear in Phys. Rev.

    Anomalous specific heat jump in the heavy fermion superconductor CeCoIn5_5

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    We study the anomalously large specific heat jump and its systematic change with pressure in CeCoIn5_5 superconductor. Starting with the general free energy functional of the superconductor for a coupled electron boson system, we derived the analytic result of the specific heat jump of the strong coupling superconductivity occurring in the coupled electron boson system. Then using the two component spin-fermion model we calculate the specific heat coefficient C(T)/TC(T)/T both for the normal and superconducting states and show a good agreement with the experiment of CeCoIn5_5. Our result also clearly demonstrated that the specific heat coefficient C(T)/TC(T)/T of a coupled electron boson system can be freely interpreted as a renormalization either of the electronic or of the bosonic degrees of freedom.Comment: 5 pages, 2 figure
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