10,309 research outputs found

### SPECTRAL CORRELATIONS IN DISORDERED ELECTRONIC SYSTEMS: CROSSOVER FROM METAL TO INSULATOR REGIME

We use the semiclassical approach combined with the scaling results for the
diffusion coefficient to consider the two-level correlation function
$R(\varepsilon)$ for a disordered electron system in the crossover region,
characterized by the appearance of a macroscopic correlation or localization
length, $\xi$, that diverges at the metal-insulator transition. We show new
critical statistics, characterized by a nontrivial asymptotic behavior of
$R(\varepsilon)$, to emerge on both sides of the transition at higher energies,
and to expand to all energies larger than mean level spacing when $\xi$ exceeds
the system size.Comment: 4 pages,1 figure, in self-ectracting uuencoded gz-compressed file to
be published in Phys. Rev. Letters; REVTeX source file is available upon
reques

### The Level Spacing Distribution Near the Anderson Transition

For a disordered system near the Anderson transition we show that the
nearest-level-spacing distribution has the asymptotics $P(s)\propto \exp(-A
s^{2-\gamma })$ for s\gg \av{s}\equiv 1 which is universal and intermediate
between the Gaussian asymptotics in a metal and the Poisson in an insulator.
(Here the critical exponent $0<\gamma<1$ and the numerical coefficient $A$
depend only on the dimensionality $d>2$). It is obtained by mapping the energy
level distribution to the Gibbs distribution for a classical one-dimensional
gas with a pairwise interaction. The interaction, consistent with the universal
asymptotics of the two-level correlation function found previously, is proved
to be the power-law repulsion with the exponent $-\gamma$.Comment: REVTeX, 8 pages, no figure

### Low-Temperature Decoherence of Qubit Coupled to Background Charges

We have found an exact expression for the decoherence rate of a Josephson
charge qubit coupled to fluctuating background charges. At low temperatures $T$
the decoherence rate ${\Gamma}$ is linear in $T$ while at high temperatures it
saturates in agreement with a known classical solution which, however, reached
at surprisingly high $T$. In contrast to the classical picture, impurity states
spread in a wide interval of energies ($\gg T$) may essentially contribute to
${\Gamma}$.Comment: Both figures are changed to illustrate a more generic case of
impurity states spread in wide interval of energies. Some changes have been
made to the abstract and the introductio

### Pseudo diamagnetism of four component exciton condensates

We analyze the spin structure of the ground state of four-component exciton
condensates in coupled quantum wells as a function of spin-dependent
interactions and applied magnetic field. The four components correspond to the
degenerate exciton states characterized by $\pm2$ and $\pm1$ spin projections
to the axis of the structure. We show that in a wide range of parameters, the
chemical potential of the system increases as a function of magnetic field,
which manifests a pseudo-diamagnetism of the system. The transitions to
polarized two- and one-component condensates can be of the first-order in this
case. The predicted effects are caused by energy conserving mixing of $\pm2$
and $\pm1$ excitons.Comment: 4 pages, 2 figure

### Use of LARS system for the quantitative determination of smoke plume lateral diffusion coefficients from ERTS images of Virginia

A technique for measuring smoke plume of large industrial sources observed by satellite using LARSYS is proposed. A Gaussian plume model is described, integrated in the vertical, and inverted to yield a form for the lateral diffusion coefficient, Ky. Given u, wind speed; y sub l, the horizontal distance of a line of constant brightness from the plume symmetry axis a distance x sub l, downstream from reference point at x=x sub 2, y=0, then K sub y = u ((y sub 1) to the 2nd power)/2 x sub 1 1n (x sub 2/x sub 1). The technique is applied to a plume from a power plant at Chester, Virginia, imaged August 31, 1973 by LANDSAT I. The plume bends slightly to the left 4.3 km from the source and estimates yield Ky of 28 sq m/sec near the source, and 19 sq m/sec beyond the bend. Maximum ground concentrations are estimated between 32 and 64 ug/cu m. Existing meteorological data would not explain such concentrations

### Do Athermal Amorphous Solids Exist?

We study the elastic theory of amorphous solids made of particles with finite
range interactions in the thermodynamic limit. For the elastic theory to exist
one requires all the elastic coefficients, linear and nonlinear, to attain a
finite thermodynamic limit. We show that for such systems the existence of
non-affine mechanical responses results in anomalous fluctuations of all the
nonlinear coefficients of the elastic theory. While the shear modulus exists,
the first nonlinear coefficient B_2 has anomalous fluctuations and the second
nonlinear coefficient B_3 and all the higher order coefficients (which are
non-zero by symmetry) diverge in the thermodynamic limit. These results put a
question mark on the existence of elasticity (or solidity) of amorphous solids
at finite strains, even at zero temperature. We discuss the physical meaning of
these results and propose that in these systems elasticity can never be
decoupled from plasticity: the nonlinear response must be very substantially
plastic.Comment: 11 pages, 11 figure

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