154 research outputs found
Correlations in Transmission of Light through a Disordered Amplifying Medium
The angular and frequency correlation functions of the transmission
coefficient for light propagation through a strongly scattering amplifying
medium are considered. It is found that just as in the case of an elastic
scattering medium the correlation function consists of three terms. However,
the structure of the terms is rather different. Angular correlation has a
power-law decay and exhibits oscillations. There is no "memory effect" as in
the case of an elastic medium. Interaction between diffusion modes is strongly
enhanced near the lasing threshold. Frequency correlation scale decreases close
to the lasing threshold.
We also consider time correlations of the transmission in the case of
nonstationary inhomogeneities. We find short- and long-range time correlations.
The scale of the short-range correlation decreases, while the long-range
correlation scale becomes infinite near the threshold.Comment: 16 pages, 7 postscript figure
Statistics of speckle patterns
We develop a general method for calculating statistical properties of the
speckle pattern of coherent waves propagating in disordered media. In some
aspects this method is similar to the Boltzmann-Langevin approach for the
calculation of classical fluctuations. We apply the method to the case where
the incident wave experiences many small angle scattering events during
propagation, but the total angle change remains small. In many aspects our
results for this case are different from results previously known in the
literature. The correlation function of the wave intensity at two points
separated by a distance , has a long range character. It decays as a power
of and changes sign. We also consider sensitivities of the speckles to
changes of external parameters, such as the wave frequency and the incidence
angle.Comment: 4 pages, 2 figure
Point contact spectroscopy of hopping transport: effects of a magnetic field
The conductance of a point contact between two hopping insulators is expected
to be dominated by the individual localized states in its vicinity. Here we
study the additional effects due to an external magnetic field. Combined with
the measured conductance, the measured magnetoresistance provides detailed
information on these states (e.g. their localization length, the energy
difference and the hopping distance between them). We also calculate the
statistics of this magnetoresistance, which can be collected by changing the
gate voltage in a single device. Since the conductance is dominated by the
quantum interference of particular mesoscopic structures near the point
contact, it is predicted to exhibit Aharonov-Bohm oscillations, which yield
information on the geometry of these structures. These oscillations also depend
on local spin accumulation and correlations, which can be modified by the
external field. Finally, we also estimate the mesoscopic Hall voltage due to
these structures.Comment: 7 pages, 5 figur
Tunneling between 2D electron layers with correlated disorder: anomalous sensitivity to spin-orbit coupling
Tunneling between two-dimensional electron layers with mutually correlated
disorder potentials is studied theoretically. Due to this correlation, the
diffusive eigenstates in different layers are almost orthogonal to each other.
As a result, a peak in the tunnel I-V characteristics shifts towards small
bias, V. This "protects" the peak against the interaction-induced smearing,
since the relaxation rate near the Fermi level is low. If the correlation in
disorder potentials is complete, the peak position and width are governed by
the spin-orbit coupling in the layers; this coupling lifts the orthogonality of
the eigenstates. Possibility to use inter-layer tunneling for experimental
determination of weak intrinsic spin-orbit splitting of the Fermi surface is
discussed.Comment: 5 pages, 5 figures; published version, minor change
Concentration dependence of the transition temperature in metallic spin glasses
The dependence of the transition temperature in terms of the
concentration of magnetic impurities in spin glasses is explained on the
basis of a screened RKKY interaction. The two observed power laws, at
low and for intermediate , are described in a unified
approach.Comment: 4 page
A new redback pulsar candidate 4FGL J2054.2+6904
The Fermi catalogue contains about 2000 unassociated -ray sources.
Some of them were recently identified as pulsars, including so called redbacks
and black widows, which are millisecond pulsars in tight binary systems with
non- and partially-degenerate low-mass stellar companions irradiated by the
pulsar wind. We study a likely optical and X-ray counterpart of the Fermi
source 4FGL J2054.2+6904 proposed earlier as a pulsar candidate. We use
archival optical data as well as Swift/XRT and SRG/eROSITA X-ray data to
clarify its nature. Using Zwicky Transient Facility data in and bands
spanning over 4.7 years, we find a period of 7.5 h. The folded light
curve has a smooth sinusoidal shape with the peak-to-peak amplitude of
0.4 mag. The spectral fit to the optical spectral energy distribution
of the counterpart candidate gives the star radius of 0.50.1 and
temperature of 5500300 K implying a G2--G9-type star. Its X-ray spectrum
is well fitted by an absorbed power law with the photon index of 1.00.3
and unabsorbed flux of erg s cm. All
the properties of 4FGL J2054.26904 and its presumed counterpart suggest that
it is a member of the redback family.Comment: Accepted for publication in MNRAS, 6 pages, 6 figure
Nuclear-spin qubits interaction in mesoscopic wires and rings
Theoretical study of the indirect coupling of nuclear spins (qubits) embedded
into a mesoscopic ring and in a finite length quantum wire in a magnetic field
is presented. It is found that the hyperfine interaction, via the conduction
electrons, between nuclear spins exhibits sharp maxima as function of the
magnetic field and nuclear spin positions. This phenomenon can be used for
manipulation of qubits with almost atomic precision. Experimental feasibility
and implications for quantum logics devices is discussed.Comment: 3 figures, 12 page
Statistical Properties of the Reflectance and Transmittance of an Amplifying Random Media
Statistical properties of the transmittance () and reflectance () of an
amplifying layer with one-dimensional disorder are investigated analytically.
Whereas the transmittance at typical realizations decreases exponentially with
the layer thickness just as it does in absorbing media, the average
and \ are shown to
be infinite even for finite due to the contribution of low-probable
resonant realizations corresponding to the non-Gaussian tail of the
distribution of . This tail differs drastically from that in the case of
absorption. The physical meaning of typical and resonant realizations is
discussed.Comment: 5 pages (RevTeX
Edge spin accumulation in a ballistic regime
We consider a mesoscopic {\it ballistic} structure with Rashba spin-orbit
splitting of the electron spectrum. The ballistic region is attached to the
leads with a voltage applied between them. We calculate the edge spin density
which appears in the presence of a charge current through the structure due to
the difference in populations of electrons coming from different leads.
Combined effect of the boundary scattering and spin precession leads to
oscillations of the edge polarization with the envelope function decaying as a
power law of the distance from the boundary. The problem is solved with the use
of scattering states. The simplicity of the method allows to gain an insight
into the underlaying physics. We clarify the role of the unitarity of
scattering for the problem of edge spin accumulation. In case of a straight
boundary it leads to exact cancellation of all long-wave oscillations of the
spin density. As a result, only the Friedel-like spin density oscillations with
the momentum 2k_F survive. However, this appears to be rather exceptional case.
In general, the smooth spin oscillations with the spin precession length
recover, as it happens, e.g., for the wiggly boundary. We demonstrate also,
that there is no relation between the spin current in the bulk, which is zero
in the considered case, and the edge spin accumulation.Comment: Latex, 6 pages, 2 fig
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