1,311 research outputs found
Inelastic Interaction Corrections and Universal Relations for Full Counting Statistics
We analyze in detail the interaction correction to Full Counting Statistics
(FCS) of electron transfer in a quantum contact originating from the
electromagnetic environment surrounding the contact. The correction can be
presented as a sum of two terms, corresponding to elastic/inelastic electron
transfer. Here we primarily focus on the inelastic correction.
For our analysis, it is important to understand more general -- universal --
relations imposed on FCS only by quantum mechanics and statistics with no
regard for a concrete realization of a contact. So we derive and analyze these
relations. We reveal that for FCS the universal relations can be presented in a
form of detailed balance. We also present several useful formulas for the
cumulants.
To facilitate the experimental observation of the effect, we evaluate
cumulants of FCS at finite voltage and temperature. Several analytical results
obtained are supplemented by numerical calculations for the first three
cumulants at various transmission eigenvalues.Comment: 10 pages, 3 figure
Coulomb interacting Dirac fermions in disordered graphene
We study interacting Dirac quasiparticles in disordered graphene and find
that an interplay between the unscreened Coulomb interactions and
pseudo-relativistic quasiparticle kinematics can be best revealed in the
ballistic regime, whereas in the diffusive limit the behavior is qualitatively
(albeit, not quantitatively) similar to that of the ordinary 2DEG with
parabolic dispersion. We calculate the quasiparticle width and density of
states that can be probed by photoemission, tunneling, and magnetization
measurements.Comment: Latex, 4 page
Feedback of the electromagnetic environment on current and voltage fluctuations out of equilibrium
A theory is presented for low-frequency current and voltage correlators of a
mesoscopic conductor embedded in a macroscopic electromagnetic environment.
This Keldysh field theory evaluated at its saddle-point provides the
microscopic justification for our earlier phenomenological calculation (using
the cascaded Langevin approach). The nonlinear feedback from the environment
mixes correlators of different orders, which explains the unexpected
temperature dependence of the third moment of tunneling noise observed in a
recent experiment. At non-zero temperature, current and voltage correlators of
order three and higher are no longer linearly related. We show that a Hall bar
measures voltage correlators in the longitudinal voltage and current
correlators in the Hall voltage. We go beyond the saddle-point approximation to
consider the environmental Coulomb blockade. We derive that the leading order
Coulomb blockade correction to the n-th cumulant of current fluctuations is
proportional to the voltage derivative of the (n+1)-th cumulant, generalizing
to any n the earlier results for n=1,2.Comment: 12 pages, 8 figure
Temperature dependent third cumulant of tunneling noise
Poisson statistics predicts that the shot noise in a tunnel junction has a
temperature independent third cumulant e^2\I, determined solely by the mean
current I. Experimental data, however, show a puzzling temperature dependence.
We demonstrate theoretically that the third cumulant becomes strongly
temperature dependent and may even change sign as a result of feedback from the
electromagnetic environment. In the limit of a noninvasive (zero-impedance)
measurement circuit in thermal equilibrium with the junction, we find that the
third cumulant crosses over from e^2/I at low temperatures to -e^2/I at high
temperatures.Comment: 4 pages including 2 figure
Secondary "Smile"-gap in the density of states of a diffusive Josephson junction for a wide range of contact types
The superconducting proximity effect leads to strong modifications of the
local density of states in diffusive or chaotic cavity Josephson junctions,
which displays a phase-dependent energy gap around the Fermi energy. The
so-called minigap of the order of the Thouless energy is
related to the inverse dwell time in the diffusive region in the limit
, where is the superconducting energy gap.
In the opposite limit of a large Thouless energy , a
small new feature has recently attracted attention, namely, the appearance of a
further secondary gap, which is around two orders of magnitude smaller compared
to the usual superconducting gap. It appears in a chaotic cavity just below the
superconducting gap edge and vanishes for some value of the phase
difference between the superconductors. We extend previous theory restricted to
a normal cavity connected to two superconductors through ballistic contacts to
a wider range of contact types. We show that the existence of the secondary gap
is not limited to ballistic contacts, but is a more general property of such
systems. Furthermore, we derive a criterion which directly relates the
existence of a secondary gap to the presence of small transmission eigenvalues
of the contacts. For generic continuous distributions of transmission
eigenvalues of the contacts, no secondary gap exists, although we observe a
singular behavior of the density of states at . Finally, we provide a
simple one-dimensional scattering model which is able to explain the
characteristic "smile" shape of the secondary gap.Comment: 12 pages, 12 figure
"Smile"-gap in the density of states of a cavity between superconductors
The density of Andreev levels in a normal metal () in contact with two
superconductors () is known to exhibit an induced minigap related to the
inverse dwell time. We predict a small secondary gap just below the
superconducting gap edge---a feature that has been overlooked so far in
numerous studies of the density of states in structures. In a generic
structure with being a chaotic cavity, the secondary gap is the widest at
zero phase bias. It closes at some finite phase bias, forming the shape of a
"smile". Asymmetric couplings give even richer gap structures near the phase
difference \pi. All the features found should be amendable to experimental
detection in high-resolution low-temperature tunneling spectroscopy.Comment: 5 pages, 4 figure
The Effect of Mechanical Resonance on Josephson Dynamics
We study theoretically dynamics in a Josephson junction coupled to a
mechanical resonator looking at the signatures of the resonance in d.c.
electrical response of the junction. Such a system can be realized
experimentally as a suspended ultra-clean carbon nanotube brought in contact
with two superconducting leads. A nearby gate electrode can be used to tune the
junction parameters and to excite mechanical motion. We augment theoretical
estimations with the values of setup parameters measured in the samples
fabricated.
We show that charging effects in the junction give rise to a mechanical force
that depends on the superconducting phase difference. The force can excite the
resonant mode provided the superconducting current in the junction has
oscillating components with a frequency matching the resonant frequency of the
mechanical resonator. We develop a model that encompasses the coupling of
electrical and mechanical dynamics. We compute the mechanical response (the
effect of mechanical motion) in the regime of phase bias and d.c. voltage bias.
We thoroughly investigate the regime of combined a.c. and d.c. bias where
Shapiro steps are developed and reveal several distinct regimes characteristic
for this effect. Our results can be immediately applied in the context of
experimental detection of the mechanical motion in realistic superconducting
nano-mechanical devices.Comment: 18 pages, 11 figure
Full Current Statistics in Diffusive Normal-Superconductor Structures
We study the current statistics in normal diffusive conductors in contact
with a superconductor. Using an extension of the Keldysh Green's function
method we are able to find the full distribution of charge transfers for all
temperatures and voltages. For the non-Gaussian regime, we show that the
equilibrium current fluctuations are enhanced by the presence of the
superconductor. We predict an enhancement of the nonequilibrium current noise
for temperatures below and voltages of the order of the Thouless energy
E_Th=D/L^2. Our calculation fully accounts for the proximity effect in the
normal metal and agrees with experimental data. We demonstrate that the
calculation of the full current statistics is in fact simpler than a concrete
calculation of the noise.Comment: 4 pages, 2 figures (included
Hierarchical Wigner Crystal at the Edge of Quantum Hall Bar
We show that quasiholes persist near the edge of incompressible Quantum Hall
state forming a Wigner structure. The average density of quasiholes is fixed by
electrostatics and decreases slowly with increasing distance from the edge. As
we see from elementary reasoning, their specific arrangement can not be a
regular Wigner lattice and shows a complex hierarchical structure of
dislocations.Comment: LaTEX file. Ps figures upon reques
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