5,655 research outputs found

    RANDOM MATRIX THEORY APPROACH TO THE INTENSITY DISTRIBUTIONS OF WAVES PROPAGATING IN A RANDOM MEDIUM

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    Statistical properties of coherent radiation propagating in a quasi - 1D random media is studied in the framework of random matrix theory. Distribution functions for the total transmission coefficient and the angular transmission coefficient are obtained.Comment: 8 pages, latex, no figures. Submitted to Phys.Rev.

    Free energy and torque for superconductors with different anisotropies of H_{c2} and lambda

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    The free energy is evaluated for a uniaxial superconductor with the anisotropy of the upper critical field, gamma_H = H_{c2,ab}/H_{c2,c}, different from the anisotropy of the penetration depth gamma_{lambda} = lambda_c/lambda_{ab}. With increasing difference between gamma_H and gamma_{lambda}, the equilibrium orientation of the crystal relative to the applied field may shift from theta = pi/2 (theta is the angle between the field and the c axis) to lower angles and reach theta = 0 for large enough gamma_H. These effects are expected to take place in MgB_2.Comment: 4 pages, 3 fig

    Frequency dependent third cumulant of current in diffusive conductors

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    We calculate the frequency dispersion of the third cumulant of current in diffusive-metal contacts. The cumulant exhibits a dispersion at the inverse time of diffusion across the contact, which is typically much smaller than the inverse RCRC time. This dispersion is much more pronounced in the case of strong electron-electron scattering than in the case of purely elastic scattering because of a different symmetry of the relevant second-order correlation functions.Comment: 8 pages, 4 figure

    Statistics of fluctuations for two types of crossover: from ballistic to diffusive regime and from orthogonal to unitary ensemble

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    In our previous publication [Kogan et al, Phys. Rev. {\bf 48}, 9404 (1993)] we considered the issue of statistics of radiation diffusively propagating in a disordered medium. The consideration was in the framework of diagrammatic techniques and a new representation for the intensity distribution function in terms of connected diagrams only was proposed. Here we use similar approach to treat the issue of statistics in the regime of the crossover between ballistic and diffusive transport. We find that even small contribution from coherent component decreases by one half the intensity distribution function for small values of intensity and also produces oscillations of the distribution function. We also apply this method to study statistics of fluctuations of wave functions of chaotic electrons in a quantum dot in an arbitrary magnetic field, by calculating the single state local density in the regime of the crossover between the orthogonal and unitary ensemble.Comment: Revtex, 3 pages + 2 ps.figures in uuencoded file, a version which clarifies and unites the results of two previous submission

    Current fluctuations in a spin filter with paramagnetic impurities

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    We analyze the frequency dependence of shot noise in a spin filter consisting of a normal grain and ferromagnetic electrodes separated by tunnel barriers. The source of frequency-dependent noise is random spin-flip electron scattering that results from spin-orbit interaction and magnetic impurities. Though the latter mechanism does not contribute to the average current, it contributes to the noise and leads to its dispersion at frequencies of the order of the Korringa relaxation rate. Under nonequilibrium conditions, this rate is proportional to the applied bias VV, but parametrically smaller than eV/eV/\hbar.Comment: 6 pages, 2 figure

    Reply to [arXiv:1201.5347] "Comment on 'Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors'"

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    We argue that cutoff in the London model cannot be settled without use of the microscopic theory

    Current fluctuations near to the 2D superconductor-insulator quantum critical point

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    Systems near to quantum critical points show universal scaling in their response functions. We consider whether this scaling is reflected in their fluctuations; namely in current-noise. Naive scaling predicts low-temperature Johnson noise crossing over to noise power Ez/(z+1)\propto E^{z/(z+1)} at strong electric fields. We study this crossover in the metallic state at the 2d z=1 superconductor/insulator quantum critical point. Using a Boltzmann-Langevin approach within a 1/N-expansion, we show that the current noise obeys a scaling form Sj=TΦ[T/Teff(E)]S_j=T \Phi[T/T_{eff}(E)] with TeffET_{eff} \propto \sqrt{E}. We recover Johnson noise in thermal equilibrium and SjES_j \propto \sqrt{E} at strong electric fields. The suppression from free carrier shot noise is due to strong correlations at the critical point. We discuss its interpretation in terms of a diverging carrier charge 1/E\propto 1/\sqrt{E} or as out-of-equilibrium Johnson noise with effective temperature E\propto \sqrt{E}.Comment: 5 page

    Non-linear bigravity and cosmic acceleration

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    We explore the cosmological solutions of classes of non-linear bigravity theories. These theories are defined by effective four-dimensional Lagrangians describing the coupled dynamics of two metric tensors, and containing, in the linearized limit, both a massless graviton and an ultralight one. We focus on two paradigmatic cases: the case where the coupling between the two metrics is given by a Pauli-Fierz-type mass potential, and the case where this coupling derives from five-dimensional brane constructions. We find that cosmological evolutions in bigravity theories can be described in terms of the dynamics of two ``relativistic particles'', moving in a curved Lorenzian space, and connected by some type of nonlinear ``spring''. Classes of bigravity cosmological evolutions exhibit a ``locking'' mechanism under which the two metrics ultimately stabilize in a bi-de-Sitter configuration, with relative (constant) expansion rates. In the absence of matter, we find that a generic feature of bigravity cosmologies is to exhibit a period of cosmic acceleration. This leads us to propose bigravity as a source of a new type of dark energy (``tensor quintessence''), exhibiting specific anisotropic features. Bigravity could also have been the source of primordial inflation.Comment: 55 pages, 4 figures, references and comments added, final version published in Phys. Rev.
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