10,691 research outputs found
Impact of incomplete ionization of dopants on the electrical properties of compensated p-type silicon
This paper investigates the importance of incomplete ionization of dopants in compensated p-type Si and its impact on the majority-carrier density and mobility and thus on the resistivity. Both theoretical calculations and temperature-dependent Hall-effect measurements demonstrate that the carrier density is more strongly affected by incomplete ionization in compensated Si than in uncompensated Si with the same net doping. The previously suggested existence of a compensation-specific scattering mechanism to explain the reduction of mobility in compensated Si is shown not to be consistent with the T-dependence of the measuredcarrier mobility. The experiment also shows that, in the vicinity of 300 K, the resistivity of compensated Si has a much weaker dependence on temperature than that of uncompensated silicon
Dielectric response of Anderson and pseudogapped insulators
Using a combination of analytic and numerical methods, we study the
polarizability of a (non-interacting) Anderson insulator in one, two, and three
dimensions and demonstrate that, in a wide range of parameters, it scales
proportionally to the square of the localization length, contrary to earlier
claims based on the effective-medium approximation. We further analyze the
effect of electron-electron interactions on the dielectric constant in
quasi-1D, quasi-2D and 3D materials with large localization length, including
both Coulomb repulsion and phonon-mediated attraction. The phonon-mediated
attraction (in the pseudogapped state on the insulating side of the
Superconductor-Insulator Transition) produces a correction to the dielectric
constant, which may be detected from a linear response of a dielectric constant
to an external magnetic field.Comment: 9 page
Critical generalized inverse participation ratio distributions
The system size dependence of the fluctuations in generalized inverse
participation ratios (IPR's) at criticality is investigated
numerically. The variances of the IPR logarithms are found to be
scale-invariant at the macroscopic limit. The finite size corrections to the
variances decay algebraically with nontrivial exponents, which depend on the
Hamiltonian symmetry and the dimensionality. The large- dependence of the
asymptotic values of the variances behaves as according to theoretical
estimates. These results ensure the self-averaging of the corresponding
generalized dimensions.Comment: RevTex4, 5 pages, 4 .eps figures, to be published in Phys. Rev.
Numerical study of relaxation in electron glasses
We perform a numerical simulation of energy relaxation in three-dimensional
electron glasses in the strongly localized regime at finite temperatures. We
consider systems with no interactions, with long-range Coulomb interactions and
with short-range interactions, obtaining a power law relaxation with an
exponent of 0.15, which is independent of the parameters of the problem and of
the type of interaction. At very long times, we always find an exponential
regime whose characteristic time strongly depends on temperature, system size,
interaction type and localization radius. We extrapolate the longest relaxation
time to macroscopic sizes and, for interacting samples, obtain values much
larger than the measuring time. We finally study the number of electrons
participating in the relaxation processes of very low energy configurations.Comment: 6 eps figures. To be published in Phys. Rev.
Anderson transition in systems with chiral symmetry
Anderson localization is a universal quantum feature caused by destructive
interference. On the other hand chiral symmetry is a key ingredient in
different problems of theoretical physics: from nonperturbative QCD to highly
doped semiconductors. We investigate the interplay of these two phenomena in
the context of a three-dimensional disordered system. We show that chiral
symmetry induces an Anderson transition (AT) in the region close to the band
center. Typical properties at the AT such as multifractality and critical
statistics are quantitatively affected by this additional symmetry. The origin
of the AT has been traced back to the power-law decay of the eigenstates; this
feature may also be relevant in systems without chiral symmetry.Comment: RevTex4, 4 two-column pages, 3 .eps figures, updated references,
final version as published in Phys. Rev.
A first study of the galaxy HRG 2304 and its companion AM 1646-795 (NED01)
Aims. We report the first study of the peculiar ring-like galaxy HRG 2304
(NED02),which was previously classified as a ring galaxy with an elliptical
smooth ring. This object was selected to prove that it is a candidate for the
Solitaire-type ring galaxies in an early stage of ring formation. The main goal
of this work is to provide the spectral characteristics of the current object
and its companion AM 1646-795 (NED01). Methods. The study is based on
spectroscopic observations in the optical band to highlight the characteristics
of this interacting galaxy. To investigate the star formation history of HRG
2304 we used the stellar population synthesis code STARLIGHT. The direct V and
B broad band images were used to enhance some fine structures. Results. Along
the entire long-slit signal, the spectra of HRG 2304 and its companion resemble
that of an early-type galaxy. We estimated a heliocentric systemic redshift of
z = 0.0415, corresponding to heliocentric velocities of 12449 km s-1 for HRG
2304 (NED02) and 12430 km s-1 for AM1646-795 (NED01). The spatial variation in
the contribution of the stellar population components for both objects are
dominated by an old stellar population 2x10^9 < t < 13x10^9 yr. The observed
radial-velocity distribution and the fine structures around HRG 2304 suggest an
ongoing tidal interaction of both galaxies. Conclusions.The spectroscopic
results and the morphological peculiarities of HRG 2304 can be adequately
interpreted as an ongoing interaction with the companion galaxy. Both galaxies
are early-type, the companion is elliptical, and the smooth distribution of the
material around HRG 2304 and its off-center nucleus in the direction of
AM1646-795 (NED01) characterize HRG 2304 as a Solitaire-type galaxy candidate
in an early stage of ring formation.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10
figures and 3 table
Level number variance and spectral compressibility in a critical two-dimensional random matrix model
We study level number variance in a two-dimensional random matrix model
characterized by a power-law decay of the matrix elements. The amplitude of the
decay is controlled by the parameter b. We find analytically that at small
values of b the level number variance behaves linearly, with the
compressibility chi between 0 and 1, which is typical for critical systems. For
large values of b, we derive that chi=0, as one would normally expect in the
metallic phase. Using numerical simulations we determine the critical value of
b at which the transition between these two phases occurs.Comment: 6 page
Multifractality of Hamiltonians with power-law transfer terms
Finite-size effects in the generalized fractal dimensions 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 on
is found in both regimes for values of q \alt 4g^{-1}, where is the
coupling constant of the model.Comment: RevTex4, 5 two-column pages, 5 .eps figures, to be published in Phys.
Rev.
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