9,792 research outputs found
Magnetoconductance of carbon nanotube p-n junctions
The magnetoconductance of p-n junctions formed in clean single wall carbon
nanotubes is studied in the noninteracting electron approximation and
perturbatively in electron-electron interaction, in the geometry where a
magnetic field is along the tube axis. For long junctions the low temperature
magnetoconductance is anomalously large: the relative change in the conductance
becomes of order unity even when the flux through the tube is much smaller than
the flux quantum. The magnetoconductance is negative for metallic tubes. For
semiconducting and small gap tubes the magnetoconductance is nonmonotonic;
positive at small and negative at large fields.Comment: 5 pages, 2 figure
Two-photon correlations as a sign of sharp transition in quark-gluon plasma
The photon production arising due to time variation of the medium has been
considered. The Hamilton formalism for photons in time-variable medium (plasma)
has been developed with application to inclusive photon production. The results
have been used for calculation of the photon production in the course of
transition from quark-gluon phase to hadronic phase in relativistic heavy ion
collisions. The relative strength of the effect as well as specific two- photon
correlations have been evaluated. It has been demonstrated that the opposite
side two-photon correlations are indicative of the sharp transition from the
quark-gluon phase to hadrons.Comment: 23 pages, 2 figure
Spin resolved Andreev reflection in ferromagnet-superconductor junctions with Zeeman splitting
Andreev reflection in ferromagnet-superconductor junctions is derived in a
regime in which Zeeman splitting dominates the response of the superconductor
to an applied magnetic field. Spin-up and spin-down Andreev reflections are
shown to be resolved as voltage is increased. In the metallic limit, the
transition from Andreev to tunnel conductivity in the spin-up channels has a
non trivial behavior when spin polarization is increased. The conductance is
asymmetric in a voltage reversal.Comment: RevTex. 13 pages. 3 figures include
On the spectrum of facet crystallization waves at the smooth 4He crystal surface
The wavelike processes of crystallization and melting or crystallization
waves are well known to exist at the 4He crystal surface in the rough state.
Much less is known about crystallization waves for the 4He crystal surface in
the smooth well-faceted state below the roughening transition temperature. To
meet the lack, we analyze here the spectrum of facet crystallization waves and
its dependence upon the wavelength, perturbation amplitude, and the number of
possible facet steps distributed somehow over the wavelength. All the
distinctive features of facet crystallization waves from conventional waves at
the rough surface result from a nonanalytic cusplike behavior in the angle
dependence for the surface tension of smooth crystal facets.Comment: 7 pages, 3 figures, 1 tabl
Improved Limit on the Electric Dipole Moment of the Electron
The standard model of particle physics accurately describes all particle physics measurements made so far in the laboratory. However, it is unable to answer many questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories that contain particles and interactions beyond the standard model, such as models that incorporate supersymmetry, may explain these phenomena. Such particles appear in the vacuum and interact with common particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which could explain the cosmological matter–antimatter asymmetry, can give rise to an electric dipole moment along the spin axis of the electron. No electric dipole moments of fundamental particles have been observed. However, dipole moments only slightly smaller than the current experimental bounds have been predicted to arise from particles more massive than any known to exist. Here we present an improved experimental limit on the electric dipole moment of the electron, obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field. The sensitivity of our measurement is more than one order of magnitude better than any previous measurement. This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider
Frobenius-Perron Resonances for Maps with a Mixed Phase Space
Resonances of the time evolution (Frobenius-Perron) operator P for phase
space densities have recently been shown to play a key role for the
interrelations of classical, semiclassical and quantum dynamics. Efficient
methods to determine resonances are thus in demand, in particular for
Hamiltonian systems displaying a mix of chaotic and regular behavior. We
present a powerful method based on truncating P to a finite matrix which not
only allows to identify resonances but also the associated phase space
structures. It is demonstrated to work well for a prototypical dynamical
system.Comment: 5 pages, 2 figures, 2nd version as published (minor changes
Superflow in Solid 4He
Kim and Chan have recently observed Non-Classical Rotational Inertia (NCRI)
for solid He in Vycor glass, gold film, and bulk. Their low value of
the superfluid fraction, , is consistent with what
is known of the atomic delocalization in this quantum solid. By including a
lattice mass density distinct from the normal fluid density
, we argue that , and we
develop a model for the normal fluid density with contributions from
longitudinal phonons and ``defectons'' (which dominate). The Bose-Einstein
Condensation (BEC) and macroscopic phase inferred from NCRI implies quantum
vortex lines and quantum vortex rings, which may explain the unusually low
critical velocity and certain hysteretic phenomena.Comment: 4 page pdf, 1 figur
Self-consistent microscopic calculations for non-local transport through nanoscale superconductors
We implement self-consistent microscopic calculations in order to describe
out-of-equilibrium non-local transport in normal metal-superconductor-normal
metal hybrid structures in the presence of a magnetic field and for arbitrary
interface transparencies. A four terminal setup simulating usual experimental
situations is described by means of a tight-binding model. We present results
for the self-consistent order parameter and current profiles within the sample.
These profiles illustrate a crossover from a quasi-equilibrium to a strong
non-equilibrium situation when increasing the interface transparencies and the
applied voltages. We analyze in detail the behavior of the non-local
conductance in these two different regimes. While in quasi-equilibrium
conditions this can be expressed as the difference between elastic cotunneling
and crossed Andreev transmission coefficients, in a general situation
additional contributions due to the voltage dependence of the self-consistent
order parameter have to be taken into account. The present results provide a
first step towards a self-consistent theory of non-local transport including
non-equilibrium effects and describe qualitatively a recent experiment [Phys.
Rev. Lett. 97, 237003 (2006)].Comment: 12 pages, 14 figures, 2 figures correcte
Updated analysis of NN elastic scattering to 3 GeV
A partial-wave analysis of NN elastic scattering data has been updated to
include a number of recent measurements. Experiments carried out at the Cooler
Synchrotron (COSY) by the EDDA Collaboration have had a significant impact
above 1 GeV. Results are discussed in terms of the partial-wave and
direct-reconstruction amplitudes.Comment: 16 pages, 14 figures, 2 tables; Fig 10 error corrected; Accepted for
publication in Physical Review
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