260 research outputs found
Coherent properties of nano-electromechanical systems
We study the properties of a nano-electromechanical system in the coherent
regime, where the electronic and vibrational time scales are of the same order.
Employing a master equation approach, we obtain the stationary reduced density
matrix retaining the coherences between vibrational states. Depending on the
system parameters, two regimes are identified, characterized by either () an
{\em effective} thermal state with a temperature {\em lower} than that of the
environment or () strong coherent effects. A marked cooling of the
vibrational degree of freedom is observed with a suppression of the vibron Fano
factor down to sub-Poissonian values and a reduction of the position and
momentum quadratures.Comment: 12 pages, 11 figure
An electrical probe for mechanical vibrations in suspended carbon nanotubes
The transport properties of a suspended carbon nanotube probed by means of a
STM tip are investigated. A microscopic theory of the coupling between
electrons and mechanical vibrations is developed. It predicts a
position-dependent coupling constant, sizeable only in the region where the
vibron is located. This fact has profound consequences on the transport
properties, which allow to extract information on the location and size of the
vibrating portions of the nanotube.Comment: 11 Pages, 12 color figures, accepted for publication on Physical
Review
Mirando los despojos que produjo la colonialidad: ¿Cómo volver a ser nosotras en nuestra fortaleza? Una propuesta para reconstruir nuestro poder colectivo
El presente trabajo intenta dar cuenta de las violencias patriarcales, de raza y coloniales de la que somos y fuimos históricamente objeto las mujeres; e indagar en la posibilidad de la reconstrucción de un poder para afrontarlas: el poder comunitario que tejemos en las fuentes vitales del agua, el canto comunitario, la cocina, la ronda. Todos éstos, lugares vitales que otorgan nuevas fuerzas a las mujeres. Las preguntas iniciales versan en torno a: ¿Dónde ha quedado ese poder?, ¿ha quedado en un lugar?, ¿en un grupo de personas?. ¿Está?, ¿lo otorgamos?, ¿nos lo quitaron?. El trabajo relata como ejemplo concreto de construcción de ese poder contrahegemónico, la conformación de un colectivo de mujeres del interior de la provincia de Catamarca en reclamo de justicia por abusos y violencias sistemáticamente sufridas por ellas en entornos de impunidad patriarcal y eclesiástica
Phonon distributions of a single bath mode coupled to a quantum dot
The properties of an unconventional, single mode phonon bath coupled to a
quantum dot, are investigated within the rotating wave approximation. The
electron current through the dot induces an out of equilibrium bath, with a
phonon distribution qualitatively different from the thermal one. In selected
transport regimes, such a distribution is characterized by a peculiar selective
population of few phonon modes and can exhibit a sub-Poissonian behavior. It is
shown that such a sub-Poissonian behavior is favored by a double occupancy of
the dot. The crossover from a unequilibrated to a conventional thermal bath is
explored, and the limitations of the rotating wave approximation are discussed.Comment: 21 Pages, 7 figures, to appear in New Journal of Physics - Focus on
Quantum Dissipation in Unconventional Environment
One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6
Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.Comment: 7 pages, 6 figures including one animatio
Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides LaSrCoO
The magnetic excitations in the cuprate superconductors might be essential
for an understanding of high-temperature superconductivity. In these cuprate
superconductors the magnetic excitation spectrum resembles an hour-glass and
certain resonant magnetic excitations within are believed to be connected to
the pairing mechanism which is corroborated by the observation of a universal
linear scaling of superconducting gap and magnetic resonance energy. So far,
charge stripes are widely believed to be involved in the physics of hour-glass
spectra. Here we study an isostructural cobaltate that also exhibits an
hour-glass magnetic spectrum. Instead of the expected charge stripe order we
observe nano phase separation and unravel a microscopically split origin of
hour-glass spectra on the nano scale pointing to a connection between the
magnetic resonance peak and the spin gap originating in islands of the
antiferromagnetic parent insulator. Our findings open new ways to theories of
magnetic excitations and superconductivity in cuprate superconductors.Comment: Nature Communications 5, 5731 (2014
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