807 research outputs found
On Properties of the Isoscalar Giant Dipole Resonance
Main properties (strength function, energy-dependent transition density,
branching ratios for direct nucleon decay) of the isoscalar giant dipole
resonance in several medium-heavy mass spherical nuclei are described within a
continuum-RPA approach, taking into account the smearing effect. All model
parameters used in the calculations are taken from independent data.
Calculation results are compared with available experimental data.Comment: 12 pages, 2 figure
Superconducting single-mode contact as a microwave-activated quantum interferometer
The dynamics of a superconducting quantum point contact biased at subgap
voltages is shown to be strongly affected by a microwave electromagnetic field.
Interference among a sequence of temporally localized, microwave-induced
Landau-Zener transitions between current carrying Andreev levels results in
energy absorption and in an increase of the subgap current by several orders of
magnitude. The contact is an interferometer in the sense that the current is an
oscillatory function of the inverse bias voltage. Possible applications to
Andreev-level spectroscopy and microwave detection are discussed
Electromechanics of charge shuttling in dissipative nanostructures
We investigate the current-voltage (IV) characteristics of a model
single-electron transistor where mechanical motion, subject to strong
dissipation, of a small metallic grain is possible. The system is studied both
by using Monte Carlo simulations and by using an analytical approach. We show
that electromechanical coupling results in a highly nonlinear IV-curve. For
voltages above the Coulomb blockade threshold, two distinct regimes of charge
transfer occur: At low voltages the system behave as a static asymmetric double
junction and tunneling is the dominating charge transfer mechanism. At higher
voltages an abrupt transition to a new shuttle regime appears, where the grain
performs an oscillatory motion back and forth between the leads. In this regime
the current is mainly mediated by charges that are carried on the grain as it
moves from one lead to the other.Comment: 8 pages, 10 figures, final version to be published in PR
High-temperature excess current and quantum suppression of electronic backscattering in a 1-D system
We consider the electronic current through a one-dimensional conductor in the
ballistic transport regime and show that the quantum oscillations of a weakly
pinned single scattering target results in a temperature- and bias-voltage
independent excess current at large bias voltages. This is a genuine effect on
transport that derives from an exponential reduction of electronic
backscattering in the elastic channel due to quantum delocalization of the
scatterer and from suppression of low-energy electron backscattering in the
inelastic channels caused by the Pauli exclusion principle. We show that both
the mass of the target and the frequency of its quantum vibrations can be
measured by studying the differential conductance and the excess current. We
apply our analysis to the particular case of a weakly pinned C60 molecule
encapsulated by a single-wall carbon nanotube and find that the discussed
phenomena are experimentally observable.Comment: 4 pages, 4 figure
A nanomechanical resonator shuttling single electrons at radio frequencies
We observe transport of electrons through a metallic island on the tip of a
nanomechanical pendulum. The resulting tunneling current shows distinct
features corresponding to the discrete mechanical eigenfrequencies of the
pendulum. We report on measurements covering the temperature range from 300 K
down to 4.2 K. We explain the I-V curve, which differs from previous
theoretical predictions, with model calculations based on a Master equation
approach.Comment: 5 pages, 4 jpeg-figure
Effect of friction deformation on the structure and properties of a metastable austenitic chromium-nickel steel
Phonon relaxation of subgap levels in superconducting quantum point contacts
Superconducting quantum point contacts are known to possess two subgap states
per each propagating mode. In this note we compute the low-temperature
relaxation rate of the upper subgap state into the lower one with the emission
of an acoustic phonon. If the reflection in the contact is small, the
relaxation time may become much longer than the characteristic lifetime of a
bulk quasiparticle.Comment: REVTeX, 4 page
Trialogue on the number of fundamental constants
This paper consists of three separate articles on the number of fundamental
dimensionful constants in physics. We started our debate in summer 1992 on the
terrace of the famous CERN cafeteria. In the summer of 2001 we returned to the
subject to find that our views still diverged and decided to explain our
current positions. LBO develops the traditional approach with three constants,
GV argues in favor of at most two (within superstring theory), while MJD
advocates zero.Comment: Version appearing in JHEP; 31 pages late
Phase Dependent Thermopower in Andreev Interferometers
We report measurements of the thermopower S of mesoscopic Andreev
interferometers, which are hybrid loops with one arm fabricated from a
superconductor (Al), and one arm from a normal metal (Au). S depends on the
phase of electrons in the interferometer, oscillating as a function of magnetic
flux with a period of one flux quantum (= h/2e). The magnitude of S increases
as the temperature T is lowered, reaching a maximum around T = 0.14 K, and
decreases at lower temperatures. The symmetry of S oscillations with respect to
magnetic flux depends on the topology of the sample.Comment: 4 pages, 4 figure
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