364 research outputs found
Distribution of Wigner delay time from single channel disordered systems
We consider the scattering of an electron from a semi-infinite
one-dimensional random medium. The random medium is characterized by force,
-\d V/\d L being the basic random variable. We obtain an analytical
expression for the stationary delay time () distribution
within a random phase approximation. Our result agrees with earlier analytical
expressions, where the random potential is taken to be of different kind,
indicating universality of the delay time distribution, i.e., delay time
distribution is independent of the nature of disorder.Comment: 8 pages RevTeX, no figure
Directional dependence of spin currents induced by Aharonov-Casher phase
We have calculated the persistent spin current of an open ring induced by the
Aharonov-Casher phase. For unpolarized electrons there exist no persistent
charge currents, but persistent spin currents. We show that, in general, the
magnitude of the persistent spin current in a ring depends on the direction of
the direct current flow from one reservoir to another. The persistent spin
current is modulated by the cosine function of the spin precession angle. The
nonadiabatic Aharonov-Casher phase gives anomalous behaviors. The
Aharonov-Anandan phase is determined by the solid angle of spin precession.
When the nonadiabatic Aharonov-Anandan phase approaches a constant value with
the increase of the electric field, the periodic behavior of the spin
persistent current occurs in an adiabatic limit. In this limit the periodic
behavior of the persistent spin current could be understood by the effective
spin-dependent Aharonov-Bohm flux.Comment: 16pages, 5 postscript figures. Submitted to Phys. Rev.
Study of quantum current enhancement, eigenenergy spectra and magnetic moments in a multiply connected system at equilibrium
A multiply connected system in both its open and closed form variations but
in equilibrium is studied using quantum waveguide theory. The system exhibits
remarkable features, in its open form variation we see current enhancement,
hitherto seen only in non-equilibrium systems in absence of magnetic flux. In
its closed form analog parity effects are broken. Further we analyse the global
and local current densities of our system and also show that the orbital
magnetic response of the system calculated from the current densities (and
inherently linked to the topological configuration) is qualitatively not same
as that calculated from the eigenenergy spectra.Comment: 10 pages, 15 figures, 3 table
The conditional tunneling time for reflection using the WKB wave-function
We derive an expression for the conditional time for the reflection of a wave
from an arbitrary potential barrier using the WKB wavefunction in the barrier
region. Our result indicates that the conditional times for transmission and
reflection are equal for a symmetric barrier within the validity of the WKB
approach.Comment: 4 pages RevTeX, 1 eps figure include
Role of quantum entanglement due to a magnetic impurity on current magnification effect in mesoscopic open rings
We study the current magnification effect in presence of exchange scattering
of electron from a magnetic impurity placed in one arm of an open mesoscopic
ring. The exchange interaction causes entanglement of electron spin and
impurity spin. Earlier studies have shown that such an entanglement causes
reduction or loss of interference in the Aharonov-Bohm oscillations leading to
decoherence. We find however, that this entanglement, in contradiction to the
naive expectation of a reduction of current magnification, leads to enhancement
as well as suppression of the effect. We also observe additional novel features
like new resonances and current reversals.Comment: 5 pages RevTex, 5 figures include
Nonequilibrium Work distributions for a trapped Brownian particle in a time dependent magnetic field
We study the dynamics of a trapped, charged Brownian particle in presence of
a time dependent magnetic field. We calculate work distributions for different
time dependent protocols. In our problem thermodynamic work is related to
variation of vector potential with time as opposed to the earlier studies where
the work is related to time variation of the potentials which depends only on
the coordinates of the particle. Using Jarzynski identity and Crook's equality
we show that the free energy of the particle is independent of the magnetic
field, thus complementing the Bohr-van Leeuwen theorem. We also show that our
system exhibits a parametric resonance in certain parameter space.Comment: 4 pages and 5 figure
Entropy production, energy loss and currents in adiabatically rocked thermal ratchets
We study the nature of currents, input energy and entropy production in
different types of adiabatically rocked ratchets using the method of stochastic
energetics. The currents exhibit a peak as a function of noise strength. We
show that there is no underlying resonance or synchronisation phenomena in the
dynamics of the particle with these current peaks. This follows from the
analysis of energy loss in the medium. We also show that the maxima seen in
current as well as the total entropy production are not directly correlated.Comment: 6 pages, 7 figures Minor corrections are mad
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