1,871 research outputs found
Backflow and dissipation during the quantum decay of a metastable Fermi liquid
The particle current in a metastable Fermi liquid against a first-order phase
transition is calculated at zero temperature. During fluctuations of a droplet
of the stable phase, in accordance with the conservation law, not only does an
unperturbed current arise from the continuity at the boundary, but a backflow
is induced by the density response. Quasiparticles carrying these currents are
scattered by the boundary, yielding a dissipative backflow around the droplet.
An energy of the hydrodynamic mass flow of the liquid and a friction force
exerted on the droplet by the quasiparticles have been obtained in terms of a
potential of their interaction with the droplet.Comment: 5 pages (REVTeX), to be published in Phys. Rev.
Electron-vibration interaction in single-molecule junctions: from contact to tunneling regime
Point contact spectroscopy on a H2O molecule bridging Pt electrodes reveals a
clear crossover between enhancement and reduction of the conductance due to
electron-vibration interaction. As single channel models predict such a
crossover at transmission probability of t=0.5, we used shot noise measurements
to analyze the transmission and observed at least two channels across the
junction where the dominant channel has t=0.51+/-0.01 transmission probability
at the crossover conductance, which is consistent with the predictions for
single-channel models.Comment: 4 pages, 1 table, 4 figure
The democratic origins of the term "group analysis": Karl Mannheim's "third way" for psychoanalysis and social science.
It is well known that Foulkes acknowledged Karl Mannheim as the
first to use the term ‘group analysis’. However, Mannheim’s work is
otherwise not well known. This article examines the foundations of
Mannheim’s sociological interest in groups using the Frankfurt
School (1929–1933) as a start point through to the brief correspondence
of 1945 between Mannheim and Foulkes (previously
unpublished). It is argued that there is close conjunction between
Mannheim’s and Foulkes’s revision of clinical psychoanalysis along
sociological lines. Current renderings of the Frankfurt School
tradition pay almost exclusive attention to the American connection
(Herbert Marcuse, Eric Fromm, Theodor Adorno and Max Horkheimer)
overlooking the contribution of the English connection through
the work of Mannheim and Foulkes
Wigner Function Description of the A.C.-Transport Through a Two-Dimensional Quantum Point Contact
We have calculated the admittance of a two-dimensional quantum point contact
(QPC) using a novel variant of the Wigner distribution function (WDF)
formalism. In the semiclassical approximation, a Boltzman-like equation is
derived for the partial WDF describing both propagating and nonpropagating
electron modes in an effective potential generated by the adiabatic QPC. We
show that this quantum kinetic approach leads to the well-known stepwise
behavior of the real part of the admittance (the conductance), and of the
imaginary part of the admittance (the emittance), in agreement with the latest
results, which is determined by the number of propagating electron modes. It is
shown, that the emittance is sensitive to the geometry of the QPC, and can be
controlled by the gate voltage. We established that the emittance has
contributions corresponding to both quantum inductance and quantum capacitance.
Stepwise oscillations in the quantum inductance are determined by the harmonic
mean of the velocities for the propagating modes, whereas the quantum
capacitance is a significant mesoscopic manifestation of the non-propagating
(reflecting) modes.Comment: 23 pages (latex), 3 figure
Transmission Resonance in an Infinite Strip of Phason-Defects of a Penrose Approximant Network
An exact method that analytically provides transfer matrices in finite
networks of quasicrystalline approximants of any dimensionality is discussed.
We use these matrices in two ways: a) to exactly determine the band structure
of an infinite approximant network in analytical form; b) to determine, also
analytically, the quantum resistance of a finite strip of a network under
appropriate boundary conditions. As a result of a subtle interplay between
topology and phase interferences, we find that a strip of phason-defects along
a special symmetry direction of a low 2-d Penrose approximant, leads to the
rigorous vanishing of the reflection coefficient for certain energies. A
similar behavior appears in a low 3-d approximant. This type of ``resonance" is
discussed in connection with the gap structure of the corresponding ordered
(undefected) system.Comment: 18 pages special macros jnl.tex,reforder.tex, eqnorder.te
Estimation of Buttiker-Landauer traversal time based on the visibility of transmission current
We present a proposal for the estimation of B\"uttiker-Landauer traversal
time based on the visibility of transmission current. We analyze the tunneling
phenomena with a time-dependent potential and obtain the time-dependent
transmission current. We found that the visibility is directly connected to the
traversal time. Furthermore, this result is valid not only for rectangular
potential barrier but also for general form of potential to which the WKB
approximation is applicable . We compared these results with the numerical
values obtained from the simulation of Nelson's quantum mechanics. Both of them
fit together and it shows our method is very effective to measure
experimentally the traversal time.Comment: 12 pages, REVTeX, including 7 eps figure
Asymptotic self-consistency in quantum transport calculations
Ab initio simulations of quantum transport commonly focus on a central region which is considered to be connected to infinite leads through which the current flows. The electronic structure of these distant leads is normally obtained from an equilibrium calculation, ignoring the self-consistent response of the leads to the current. We examine the consequences of this, and show that the electrostatic potential Delta phi is effectively being approximated by the difference between electrochemical potentials Delta mu, and that this approximation is incompatible with asymptotic charge neutrality. In a test calculation for a simple metal-vacuum-metal junction, we find significant errors in the nonequilibrium properties calculated with this approximation, in the limit of small vacuum gaps. We provide a scheme by which these errors may be corrected
Excess Noise in Biased Superconducting Weak Links
Non-equilibrium excess noise of a short quasi one-dimensional constriction
between two superconductors is considered. A general expression for the
current-current correlation function valid for arbitrary temperatures and bias
voltages is derived. This formalism is applied to a current-carrying quantum
channel with perfect transparency. Contrary to a transparent channel separating
two normal conductors, a weak link between two superconductors exhibits a
finite level of noise. The source of noise is fractional Andreev scattering of
quasiparticles with energies greater than the half-width of the
superconducting gap. For high bias voltages, , the relation
between the zero-frequency limit of the noise spectrum, , and the excess
current reads . As both the excess noise and the excess current vanish linearly in
, %, their ratio being constant.Comment: 8 pages (Latex), 1 figur
Quantum transport and momentum conserving dephasing
We study numerically the influence of momentum-conserving dephasing on the
transport in a disordered chain of scatterers. Loss of phase memory is caused
by coupling the transport channels to dephasing reservoirs. In contrast to
previously used models, the dephasing reservoirs are linked to the transport
channels between the scatterers, and momentum conserving dephasing can be
investigated. Our setup provides a model for nanosystems exhibiting conductance
quantization at higher temperatures in spite of the presence of phononic
interaction. We are able to confirm numerically some theoretical predictions.Comment: 7 pages, 4 figure
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