864 research outputs found
N\'{e}el transition of lattice fermions in a harmonic trap: a real-space DMFT study
We study the magnetic ordering transition for a system of harmonically
trapped ultracold fermions with repulsive interactions in a cubic optical
lattice, within a real-space extension of dynamical mean-field theory (DMFT).
Using a quantum Monte Carlo impurity solver, we establish that
antiferromagnetic correlations are signaled, at strong coupling, by an enhanced
double occupancy. This signature is directly accessible experimentally and
should be observable well above the critical temperature for long-range order.
Dimensional aspects appear less relevant than naively expected.Comment: 4 pages, 4 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
Mott transitions in ternary flavor mixtures of ultracold fermions on optical lattices
Ternary flavor mixtures of ultracold fermionic atoms in an optical lattice
are studied in the case of equal, repulsive on-site interactions U>0. The
corresponding SU(3) invariant Hubbard model is solved numerically exactly
within dynamical mean-field theory using multigrid Hirsch-Fye quantum Monte
Carlo simulations. We establish Mott transitions close to integer filling at
low temperatures and show that the associated signatures in the compressibility
and pair occupancy persist to high temperatures, i.e., should be accessible to
experiments. In addition, we present spectral functions and discuss the
properties of a ``semi-compressible'' state observed for large U near half
filling.Comment: 4 pages, 5 figure
Shuttle-promoted nano-mechanical current switch
We investigate electron shuttling in three-terminal nanoelectromechanocal
device built on a movable metallic rod oscillating between two drains. The
device shows a double-well shaped electromechanical potential tunable by a
source-drain bias voltage. Four stationary regimes controllable by the bias are
found for this device: (i) single stable fixed point, (ii) two stable fixed
points, (iii) two limiting cycles, and (iv) single limiting cycle. In the
presence of perpendicular magnetic field the Lorentz force makes possible
switching from one electromechanical state to another. The mechanism of tunable
transitions between various stable regimes based on the interplay between
voltage controlled electromechanical instability and magnetically controlled
switching is suggested. The switching phenomenon is implemented for achieving
both a reliable \emph{active} current switch and sensoring of small variations
of magnetic field.Comment: 11 pages, 4 figure
Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance
We investigate instability and dynamical properties of nanoelectromechanical
systems represented by a single-electron device containing movable quantum dot
attached to a vibrating cantilever via asymmetric tunnel contact. The Kondo
resonance in electron tunneling between source and shuttle facilitates
self-sustained oscillations originated from strong coupling of mechanical and
electronic/spin degrees of freedom. We analyze stability diagram for
two-channel Kondo shuttling regime due to limitations given by the
electromotive force acting on a moving shuttle and find that the saturation
amplitude of oscillation is associated with the retardation effect of
Kondo-cloud. The results shed light on possible ways of experimental
realization of dynamical probe for the Kondo-cloud by using high tunability of
mechanical dissipation as well as supersensitive detection of mechanical
displacement
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