267 research outputs found

    Commensurability effects in one-dimensional Anderson localization: anomalies in eigenfunction statistics

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    The one-dimensional (1d) Anderson model (AM) has statistical anomalies at any rational point f=2a/λEf=2a/\lambda_{E}, where aa is the lattice constant and λE\lambda_{E} is the de Broglie wavelength. We develop a regular approach to anomalous statistics of normalized eigenfunctions ψ(r)\psi(r) at such commensurability points. The approach is based on an exact integral transfer-matrix equation for a generating function Φr(u,ϕ)\Phi_{r}(u, \phi) (uu and ϕ\phi have a meaning of the squared amplitude and phase of eigenfunctions, rr is the position of the observation point). The descender of the generating function Pr(ϕ)Φr(u=0,ϕ){\cal P}_{r}(\phi)\equiv\Phi_{r}(u=0,\phi) is shown to be the distribution function of phase which determines the Lyapunov exponent and the local density of states. In the leading order in the small disorder we have derived a second-order partial differential equation for the rr-independent ("zero-mode") component Φ(u,ϕ)\Phi(u, \phi) at the E=0E=0 (f=12f=\frac{1}{2}) anomaly. This equation is nonseparable in variables uu and ϕ\phi. Yet, we show that due to a hidden symmetry, it is integrable and we construct an exact solution for Φ(u,ϕ)\Phi(u, \phi) explicitly in quadratures. Using this solution we have computed moments Im=NI_{m}=N (m1m\geq 1) for a chain of the length NN \rightarrow \infty and found an essential difference between their mm-behavior in the center-of-band anomaly and for energies outside this anomaly. Outside the anomaly the "extrinsic" localization length defined from the Lyapunov exponent coincides with that defined from the inverse participation ratio ("intrinsic" localization length). This is not the case at the E=0E=0 anomaly where the extrinsic localization length is smaller than the intrinsic one.Comment: 33 pages, four figure

    Conductance fluctuations in a quantum dot under almost periodic ac pumping

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    It is shown that the variance of the linear dc conductance fluctuations in an open quantum dot under a high-frequency ac pumping depends significantly on the spectral content of the ac field. For a sufficiently strong ac field γτϕ<<1\gamma\tau_{\phi}<< 1, where 1/τϕ1/\tau_{\phi} is the dephasing rate induced by ac noise and γ\gamma is the electron escape rate, the dc conductance fluctuations are much stronger for the harmonic pumping than in the case of the noise ac field of the same intensity. The reduction factor rr in a static magnetic field takes the universal value of 2 only for the white--noise pumping. For the strictly harmonic pumping A(t)=A0cosωtA(t)=A_{0}\cos\omega t of sufficiently large intensity the variance is almost insensitive to the static magnetic field r1=2τϕγ<<1r-1= 2\sqrt{\tau_{\phi}\gamma} << 1. For the quasi-periodic ac field of the form A(t)=A0[cos(ω1t)+cos(ω2t)]A(t)=A_{0} [\cos(\omega_{1} t)+\cos(\omega_{2} t)] with ω1,2>>γ\omega_{1,2} >> \gamma and γτϕ<<1\gamma\tau_{\phi} << 1 we predict the novel effect of enchancement of conductance fluctuations at commensurate frequencies ω2/ω1=P/Q\omega_{2}/\omega_{1}=P/Q.Comment: 4 pages RevTex, 4 eps figures; the final version to appear in Phys.Rev.

    Multifractality and critical fluctuations at the Anderson transition

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    Critical fluctuations of wave functions and energy levels at the Anderson transition are studied for the family of the critical power-law random banded matrix ensembles. It is shown that the distribution functions of the inverse participation ratios (IPR) PqP_q are scale-invariant at the critical point, with a power-law asymptotic tail. The IPR distribution, the multifractal spectrum and the level statistics are calculated analytically in the limits of weak and strong couplings, as well as numerically in the full range of couplings.Comment: 14 pages, 13 eps figure

    Conductance Fluctuations of Open Quantum Dots under Microwave Radiation

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    We develop a time dependent random matrix theory describing the influence of a time-dependent perturbation on mesoscopic conductance fluctuations in open quantum dots. The effect of external field is taken into account to all orders of perturbation theory, and our results are applicable to both weak and strong fields. We obtain temperature and magnetic field dependences of conductance fluctuations. The amplitude of conductance fluctuations is determined by electron temperature in the leads rather than by the width of electron distribution function in the dot. The asymmetry of conductance with respect to inversion of applied magnetic field is the main feature allowing to distinguish the effect of direct suppression of quantum interference from the simple heating if the frequency of external radiation is larger than the temperature of the leads ωT\hbar\omega \gg T.Comment: 7 pages, 5 figure

    Measurement of xF3xF_3 and F2F_2 Structure Functions in Low Q2Q^2 Region with the IHEP-JINR Neutrino Detector

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    The isoscalar structure functions xF3xF_3 and F2F_2 are measured as functions of xx averaged over all Q2Q^2 permissible for the range of 6 to 28 GeV of incident neutrino (anti-neutrino) energy at the IHEP-JINR Neutrino Detector. The QCD analysis of xF3xF_3 structure function provides ΛMSˉ(4)=(411±200)\Lambda_{\bar{MS}}^{(4)} = (411 \pm 200) MeV under the assumption of QCD validity in the region of low Q2Q^2. The corresponding value of the strong interaction constant αS(MZ)=0.1230.013+0.010\alpha_S (M_Z) = 0.123^{+0.010}_{-0.013} agrees with the recent result of the CCFR collaboration and with the combined LEP/SLC result.Comment: 11 pages, 1 Postscript figure, LaTeX. Talk given at the 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 199

    Multifractality of Hamiltonians with power-law transfer terms

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    Finite-size effects in the generalized fractal dimensions dqd_q are investigated numerically. We concentrate on a one-dimensional disordered model with long-range random hopping amplitudes in both the strong- and the weak-coupling regime. At the macroscopic limit, a linear dependence of dqd_q on qq is found in both regimes for values of q \alt 4g^{-1}, where gg is the coupling constant of the model.Comment: RevTex4, 5 two-column pages, 5 .eps figures, to be published in Phys. Rev.

    "Level Curvature" Distribution for Diffusive Aharonov-Bohm Systems: analytical results

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    We calculate analytically the distributions of "level curvatures" (LC) (the second derivatives of eigenvalues with respect to a magnetic flux) for a particle moving in a white-noise random potential. We find that the Zakrzewski-Delande conjecture is still valid even if the lowest weak localization corrections are taken into account. The ratio of mean level curvature modulus to mean dissipative conductance is proved to be universal and equal to 2π2\pi in agreement with available numerical data.Comment: 12 pages. Submitted to Phys.Rev.

    Iodine sorption capacity of carbon fiber cloth materials and granular activated carbons

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    The sorption capacity for iodine vapors of samples of carbon fiber cloth materials 31-3, 31-6, 35-1, 35-2, and KIPT 16-00 obtained at NSC KIPT, carbon fiber cloth materials of the Saut and Busofit brands and active granular carbons ISQ-3, SKT-3, and DGF-2 has been studied. The sorption capacity of carbon fiber cloth materials of series 31-6 and KIPT 16-00 is ~ 30% higher in comparison with Saut fiber cloth and ~ 4 times higher than the characteristics of active granular carbons SKT-3 and DGF-2 it has been shown.Досліджено сорбційну ємність по парам йоду зразків карбонових тканин 31-3, 31-6, 35-1, 35-2 і ХФТІ 16-00, отриманих в ННЦ ХФТІ, карбонових тканин марок Саут і Бусофіт і сортів активованого гранульованого вугілля ISQ-3, СКТ-3 і DGF-2. Показано, що сорбційна ємність у тканин серій 31-6 і ХФТІ 16-00 на ~ 30% вище в порівнянні з тканиною Саут і в ~ 4 рази перевищує характеристики сортів активованого гранульованого вугілля СКТ-3 та DGF-2.Исследована сорбционная емкость по парам йода образцов карбоновых тканей 31-3, 31-6, 35-1, 35-2 и ХФТИ 16-00, полученных в ННЦ ХФТИ, карбоновых тканей марок Саут и Бусофит и активированных гранулированных углей ISQ-3, СКТ-3 и DGF-2. Показано, что сорбционная емкость у тканей серий 31-6 и ХФТИ 16-00 на ~ 30% выше в сравнении с тканью Саут и в ~ 4 раза превышает характеристики активных гранулированных углей СКТ-3 и DGF-2

    Development of a Momentum Determined Electron Beam in the 1 -45 GeV Range

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    A beam line for electrons with energies in the range of 1 to 45 GeV, low contamination of hadrons and muons and high intensity up to 10^6 per accelerator spill at 27 GeV was setup at U70 accelerator in Protvino, Russia. A beam tagging system based on drift chambers with 160 micron resolution was able to measure relative electron beam momentum precisely. The resolution sigma_p p was 0.13% at 45 GeV where multiple scattering is negligible. This test beam setup provided the possibility to study properties of lead tungstate crystals (PbWO_4) for the BTeV experiment at Fermilab.Comment: 12 pages, 8 figures; work done by the BTeV Electromagnetic Calorimeter grou

    f(α)f(\alpha) Multifractal spectrum at strong and weak disorder

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    The system size dependence of the multifractal spectrum f(α)f(\alpha) and its singularity strength α\alpha is investigated numerically. We focus on one-dimensional (1D) and 2D disordered systems with long-range random hopping amplitudes in both the strong and the weak disorder regime. At the macroscopic limit, it is shown that f(α)f(\alpha) is parabolic in the weak disorder regime. In the case of strong disorder, on the other hand, f(α)f(\alpha) strongly deviates from parabolicity. Within our numerical uncertainties it has been found that all corrections to the parabolic form vanish at some finite value of the coupling strength.Comment: RevTex4, 6 two-column pages, 4 .eps figures, new results added, updated references, to be published in Phys. Rev.
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