1,917 research outputs found
Adiabatic polaron dynamics and Josephson effect in a superconducting molecular quantum dot
We study the Josephson current through a resonant level coupled to a
vibration mode (local Holstein model) in the adiabatic limit of low oscillator
frequency. A semiclassical theory is then appropriate and allows us to consider
the oscillator dynamics within the Born-Oppenheimer approximation for arbitrary
electron-vibration couplings. The resulting Fokker-Planck equation has been
solved in the most relevant underdamped limit and yields the oscillator
distribution function and the Josephson current. Remarkably, a transition from
single-well to double-well behavior of the effective oscillator potential
surface is possible and can be tuned by variation of the superconducting phase
difference. The Josephson current is shown to be only weakly affected by the
electron-vibration coupling due to strong phonon localization near the bottom
of the potential surface.Comment: 11 pages, 9 figures, final version to appear in Phys. Rev.
Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
The Standard Model of particle physics assumes that the so-called fundamental
constants are universal and unchanging. Absorption lines arising in molecular
clouds along quasar sightlines offer a precise test for variations in the
proton-to-electron mass ratio, mu, over cosmological time and distance scales.
The inversion transitions of ammonia are particularly sensitive to mu compared
to molecular rotational transitions. Comparing the available ammonia spectra
observed towards the quasar B0218+357 with new, high-quality rotational
spectra, we present the first detailed measurement of mu with this technique,
limiting relative deviations from the laboratory value to |dmu/mu| <
1.8x10^{-6} (95% confidence level) at approximately half the Universe's current
age - the strongest astrophysical constraint to date. Higher-quality ammonia
observations will reduce both the statistical and systematic uncertainties in
these measurements.Comment: Science, 20th June 2008. 22 pages, 5 figures (12 EPS files), 2
tables, including Supporting Online Material; v2: Corrected reference for
laboratory mu-variation bound
Scattering theory of current-induced forces in mesoscopic systems
We develop a scattering theory of current-induced forces exerted by the
conduction electrons of a general mesoscopic conductor on slow "mechanical"
degrees of freedom. Our theory describes the current-induced forces both in and
out of equilibrium in terms of the scattering matrix of the phase-coherent
conductor. Under general nonequilibrium conditions, the resulting mechanical
Langevin dynamics is subject to both non-conservative and velocity-dependent
Lorentz-like forces, in addition to (possibly negative) friction. We illustrate
our results with a two-mode model inspired by hydrogen molecules in a break
junction which exhibits limit-cycle dynamics of the mechanical modes.Comment: 4+ pages, 1 figure; v2: minor modification
Magnetic scattering of Dirac fermions in topological insulators and graphene
We study quantum transport and scattering of massless Dirac fermions by
spatially localized static magnetic fields. The employed model describes in a
unified manner the effects of orbital magnetic fields, Zeeman and exchange
fields in topological insulators, and the pseudo-magnetic fields caused by
strain or defects in monolayer graphene. The general scattering theory is
formulated, and for radially symmetric fields, the scattering amplitude and the
total and transport cross sections are expressed in terms of phase shifts. As
applications, we study ring-shaped magnetic fields (including the Aharanov-Bohm
geometry) and scattering by magnetic dipoles.Comment: 11 pages, 4 figure
From Luttinger liquid to Altshuler-Aronov anomaly in multi-channel quantum wires
A crossover theory connecting Altshuler-Aronov electron-electron interaction
corrections and Luttinger liquid behavior in quasi-1D disordered conductors has
been formulated. Based on an interacting non-linear sigma model, we compute the
tunneling density of states and the interaction correction to the conductivity,
covering the full crossover.Comment: 15 pages, 3 figures, revised version, accepted by PR
The 125th anniversary of the first postulation of the soil origin of endophytic bacteria – a tribute to M.L.V. Galippe
In both managed and natural ecosystems, a wide range of various non-nodulating bacteria can thrive as endophytes in the plant interior, and some can be beneficial to their hosts (Hallmann and Berg 2007; Reinhold-Hurek and Hurek 2011). Colonizationmechanisms, the ecology and functioning of these endophytic bacteria as well as their interactions with plants have been investigated (Hardoim et al. 2008; Compant et al. 2010). Although the source of colonization can also be the spermosphere, anthosphere, caulosphere, and the phyllosphere,most endophytic bacteria are derived from the soil environment (Hallmann and Berg 2007; Compant et al. 2010)
Three-dimensional numerical simulation of 1GeV/Nucleon U92+ impact against atomic hydrogen
The impact of 1GeV/Nucleon U92+ projectiles against atomic hydrogen is
studied by direct numerical resolution of the time-dependent wave equation for
the atomic electron on a three-dimensional Cartesian lattice. We employ the
fully relativistic expressions to describe the electromagnetic fields created
by the incident ion. The wave equation for the atom interacting with the
projectile is carefully derived from the time-dependent Dirac equation in order
to retain all the relevant terms.Comment: 12 pages and 7 figures included in the tex
- …