698 research outputs found
Scatterer that leaves "footprints" but no "fingerprints"
We calculate the exact transmission coefficient of a quantum wire in the
presence of a single point defect at the wire's cut-off frequencies. We show
that while the conductance pattern (i.e., the scattering) is strongly affected
by the presence of the defect, the pattern is totally independent of the
defect's characteristics (i.e., the defect that caused the scattering cannot be
identified from that pattern).Comment: 4 pages, 3 figure
Resonances in a two-dimensional electron waveguide with a single delta-function scatterer
We study the conductance properties of a straight two-dimensional electron
waveguide with an s-like scatterer modeled by a single delta-function potential
with a finite number of modes. Even such a simple system exhibits interesting
resonance phenomena. These resonances are explained in terms of quasi-bound
states both by using a direct solution of the Schroedinger equation and by
studying the Green's function of the system. Using the Green's function we
calculate the survival probability as well as the power absorption and show the
influence of the quasi-bound states on these two quantities.Comment: 5 pages, 6 figures, to be published in Physical Review
Recommended from our members
Adaptive optical zoom sensor.
In order to optically vary the magnification of an imaging system, continuous mechanical zoom lenses require multiple optical elements and use fine mechanical motion to precisely adjust the separations between individual or groups of lenses. By incorporating active elements into the optical design, we have designed and demonstrated imaging systems that are capable of variable optical magnification with no macroscopic moving parts. Changing the effective focal length and magnification of an imaging system can be accomplished by adeptly positioning two or more active optics in the optical design and appropriately adjusting the optical power of those elements. In this application, the active optics (e.g. liquid crystal spatial light modulators or deformable mirrors) serve as variable focal-length lenses. Unfortunately, the range over which currently available devices can operate (i.e. their dynamic range) is relatively small. Therefore, the key to this concept is to create large changes in the effective focal length of the system with very small changes in the focal lengths of individual elements by leveraging the optical power of conventional optical elements surrounding the active optics. By appropriately designing the optical system, these variable focal-length lenses can provide the flexibility necessary to change the overall system focal length, and therefore magnification, that is normally accomplished with mechanical motion in conventional zoom lenses
Absence of charge backscattering in the nonequilibrium current of normal-superconductor structures
We study the nonequilibrium transport properties of a
normal-superconductor-normal structure, focussing on the effect of adding an
impurity in the superconducting region. Current conservation requires the
superfluid velocity to be nonzero, causing a distortion of the quasiparticle
dispersion relation within the superconductor. For weakly reflecting interfaces
we find a regime of intermediate voltages in which Andreev transmission is the
only permitted mechanism for quasiparticles to enter the superconductor.
Impurities in the superconductor can only cause Andreev reflection of these
quasiparticles and thus cannot degrade the current. At higher voltages, a state
of gapless superconductivity develops which is sensitive to the presence of
impurities.Comment: Latex file, 11 pages, 2 figures available upon request
[email protected], to be published in Journal of Physics: Condensed Matte
Personal Finance: An Interdisciplinary Profession
This commentary recommends that financial counseling and planning research, education, and practice be framed as an interdisciplinary profession called personal finance. Authors summarize the history of the profession and key theories providing the conceptual foundation. In order for the emerging profession of personal finance to achieve significant visibility and gain maturity, professionals must reach consensus on definining collective scholarship. Readers are encouraged to engage in the dialogue and comment on the call to action by contacting the lead author
New Host and County Records of the Fish Leech Cystobranchus klemmi (Hirudinida: Piscicolidae) in Arkansas
Adiabatic Dynamics of Superconducting Quantum Point Contacts
Starting from the quasiclassical equations for non-equilibrium Green's
functions we derive a simple kinetic equation that governs ac Josephson effect
in a superconducting quantum point contact at small bias voltages. In contrast
to existing approaches the kinetic equation is valid for voltages with
arbitrary time dependence. We use this equation to calculate
frequency-dependent linear conductance, and dc characteristics with
and without microwave radiation for resistively shunted quantum point contacts.
A novel feature of the characteristics is the excess current
appearing at small voltages. An important by-product of our
derivation is the analytical proof that the microscopic expression for the
current coincides at arbitrary voltages with the expression that follows from
the Bogolyubov-de Gennes equations, if one uses appropriate amplitudes of
Andreev reflection which contain information about microscopic structure of the
superconductors.Comment: 12 Pages, REVTEX 3.0, 3 figures available upon reques
Coherent quantum transport in narrow constrictions in the presence of a finite-range longitudinally polarized time-dependent field
We have studied the quantum transport in a narrow constriction acted upon by
a finite-range longitudinally polarized time-dependent electric field. The
electric field induces coherent inelastic scatterings which involve both
intra-subband and inter-sideband transitions. Subsequently, the dc conductance
G is found to exhibit suppressed features. These features are recognized as the
quasi-bound-state (QBS) features which are associated with electrons making
transitions to the vicinity of a subband bottom, of which the density of states
is singular. Having valley-like instead of dip-like structures, these QBS
features are different from the G characteristics for constrictions acted upon
by a finite-range time-modulated potential. In addition, the subband bottoms in
the time-dependent electric field region are shifted upward by an energy
proportional to the square of the electric field and inversely proportional to
the square of the frequency. This effective potential barrier is originated
from the square of the vector potential and it leads to the interesting
field-sensitive QBS features. An experimental set-up is proposed for the
observation of these features.Comment: 8 pages, 4 figure
Numerical study of the lattice vacancy effects on the single-channel electron transport of graphite ribbons
Lattice vacancy effects on electrical conductance of nanographite ribbon are
investigated by means of the Landauer approach using a tight binding model. In
the low-energy regime ribbons with zigzag boundary provide a single conducting
channel whose origin is connected with the presence of edge states. It is found
that the chemical potential dependence of conductance strongly depends on the
difference () of the number of removed A and B sublattice sites. The
large lattice vacancy with shows zero-conductance dips
in the single-channel region, however, the large lattice vacancy with
has no dip structure in this region. The connection between this
conductance rule and the Longuet-Higgins conjecture is also discussed
- …