4,885 research outputs found
Mesoscopic oscillations of the conductance of disordered metallic samples as a function of temperature
We show theoretically and experimentally that the conductance of small
disordered samples exhibits random oscillations as a function of temperature.
The amplitude of the oscillations decays as a power law of temperature, and
their characteristic period is of the order of the temperature itself
Distribution function of persistent current
We introduce a variant of the replica trick within the nonlinear sigma model
that allows calculating the distribution function of the persistent current. In
the diffusive regime, a Gaussian distribution is derived. This result holds in
the presence of local interactions as well. Breakdown of the Gaussian
statistics is predicted for the tails of the distribution function at large
deviations
Influence of trigonal warping on interference effects in bilayer graphene
Bilayer graphene (two coupled graphitic monolayers arranged according to Bernal stacking) is a two-dimensional gapless semiconductor with a peculiar electronic spectrum different from the Dirac spectrum in the monolayer material. In particular, the electronic Fermi line in each of its valleys has a strong p -> -p asymmetry due to trigonal warping, which suppresses the weak localization effect. We show that weak localization in bilayer graphene may be present only in devices with pronounced intervalley scattering, and we evaluate the corresponding magnetoresistance
Observation of mesoscopic conductance fluctuations in YBaCuO grain boundary Josephson Junctions
Magneto-fluctuations of the normal resistance R_N have been reproducibly
observed in high critical temp erature superconductor (HTS) grain boundary
junctions, at low temperatures. We attribute them to mesoscopic transport in
narrow channels across the grain boundary line. The Thouless energy appears to
be the relevant energy scale. Our findings have significant implications on
quasiparticle relaxation and coherent transport in HTS grain boundaries.Comment: Revised version, minor changes. 4 pages, 4 figure
Magnetoconductivity of low-dimensional disordered conductors at the onset of the superconducting transition
Magnetoconductivity of the disordered two- and three-dimensional
superconductors is addressed at the onset of superconducting transition. In
this regime transport is dominated by the fluctuation effects and we account
for the interaction corrections coming from the Cooper channel. In contrast to
many previous studies we consider strong magnetic fields and various
temperature regimes, which allow to resolve the existing discrepancies with the
experiments. Specifically, we find saturation of the fluctuations induced
magneto-conductivity for both two- and three-dimensional superconductors at
already moderate magnetic fields and discuss possible dimensional crossover at
the immediate vicinity of the critical temperature. The surprising observation
is that closer to the transition temperature weaker magnetic field provides the
saturation. It is remarkable also that interaction correction to
magnetoconductivity coming from the Cooper channel, and specifically the so
called Maki-Thompson contribution, remains to be important even away from the
critical region.Comment: 4 pages, 1 figur
Conductance fluctuations in quasi-two-dimensional systems: a practical view
The universal conductance fluctuations of quasi-two-dimensional systems are
analyzed with experimental considerations in mind. The traditional statistical
metrics of these fluctuations (such as variance) are shown to have large
statistical errors in such systems. An alternative characteristic is
identified, the inflection point of the correlation function in magnetic field,
which is shown to be significantly more useful as an experimental metric and to
give a more robust measure of phase coherence.Comment: 9 pages, 7 figure
Ferromagnetism of Weakly-Interacting Electrons in Disordered Systems
It was realized two decades ago that the two-dimensional diffusive Fermi
liquid phase is unstable against arbitrarily weak electron-electron
interactions. Recently, using the nonlinear sigma model developed by
Finkelstein, several authors have shown that the instability leads to a
ferromagnetic state. In this paper, we consider diffusing electrons interacting
through a ferromagnetic exchange interaction. Using the Hartree-Fock
approximation to directly calculate the electron self energy, we find that the
total energy is minimized by a finite ferromagnetic moment for arbitrarily weak
interactions in two dimensions and for interaction strengths exceeding a
critical proportional to the conductivity in three dimensions. We discuss the
relation between our results and previous ones
Uninformed sacrifice: evidence against long-range alarm transmission in foraging ants exposed to a localized perturbation
It is well stablished that danger information can be transmitted by ants
through relatively small distances, provoking either a state of alarm when they
move away from potentially dangerous stimulus, or charge toward it
aggressively. There is almost no knowledge if danger information can be
transmitted along large distances. In this paper, we perturb leaf cutting ants
of the species Atta insularis while they forage in their natural evioronment at
a certain point of the foraging line, so ants make a "U" turn to escape from
the danger zone and go back to the nest. Our results strongly suggest that
those ants do not transmit "danger information" to other nestmates marching
towards the danger area. The individualistic behavior of the ants returning
from the danger zone results in a depression of the foraging activity due to
the systematic sacrifice of non-informed individuals.Comment: 5 pages, 2 figure
Coulomb drag at zero temperature
We show that the Coulomb drag effect exhibits saturation at small
temperatures, when calculated to the third order in the interlayer
interactions. The zero-temperature transresistance is inversely proportional to
the third power of the dimensionless sheet conductance. The effect is therefore
the strongest in low mobility samples. This behavior should be contrasted with
the conventional (second order) prediction that the transresistance scales as a
certain power of temperature and is almost mobility-independent. The result
demonstrates that the zero-temperature drag is not an unambiguous signature of
a strongly-coupled state in double-layer systems.Comment: 4 pages, 2 figure
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