1,394 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
Overtones of Isoscalar Giant Resonances in medium-heavy and heavy nuclei
A semi-microscopic approach based on both the
continum-random-phase-approximation (CRPA) method and a phenomenological
treatment of the spreading effect is extended and applied to describe the main
properties (particle-hole strength distribution, energy-dependent transition
density, partial direct-nucleon-decay branching ratios) of the isoscalar giant
dipole, second monopole, and second quadrupole resonances. Abilities of the
approach are checked by description of gross properties of the main-tone
resonances. Calculation results obtained for the resonances in a few singly-
and doubly-closed-shell nuclei are compared with available experimental data.Comment: 12 pages, 14 figures, submitted to Phys. Rev.
Cooling of a suspended nanowire by an AC Josephson current flow
We consider a nanoelectromechanical Josephson junction, where a suspended
nanowire serves as a superconducting weak link, and show that an applied DC
bias voltage an result in suppression of the flexural vibrations of the wire.
This cooling effect is achieved through the transfer of vibronic energy quanta
first to voltage driven Andreev states and then to extended quasiparticle
electronic states. Our analysis, which is performed for a nanowire in the form
of a metallic carbon nanotube and in the framework of the density matrix
formalism, shows that such self-cooling is possible down to a level where the
average occupation number of the lowest flexural vibration mode of the nanowire
is .Comment: 4 pages, 3 figure
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