33,891 research outputs found
Disorderless quasi-localization of polar gases in one-dimensional lattices
One-dimensional polar gases in deep optical lattices present a severely
constrained dynamics due to the interplay between dipolar interactions, energy
conservation, and finite bandwidth. The appearance of dynamically-bound
nearest-neighbor dimers enhances the role of the dipolar tail,
resulting, in the absence of external disorder, in quasi-localization via dimer
clustering for very low densities and moderate dipole strengths. Furthermore,
even weak dipoles allow for the formation of self-bound superfluid lattice
droplets with a finite doping of mobile, but confined, holons. Our results,
which can be extrapolated to other power-law interactions, are directly
relevant for current and future lattice experiments with magnetic atoms and
polar molecules.Comment: 5 + 2 Page
Interface States in Carbon Nanotube Junctions: Rolling up graphene
We study the origin of interface states in carbon nanotube intramolecular
junctions between achiral tubes. By applying the Born-von Karman boundary
condition to an interface between armchair- and zigzag-terminated graphene
layers, we are able to explain their number and energies. We show that these
interface states, costumarily attributed to the presence of topological
defects, are actually related to zigzag edge states, as those of graphene
zigzag nanoribbons. Spatial localization of interface states is seen to vary
greatly, and may extend appreciably into either side of the junction. Our
results give an alternative explanation to the unusual decay length measured
for interface states of semiconductor nanotube junctions, and could be further
tested by local probe spectroscopies
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Berry phases and zero-modes in toroidal topological insulator
An effective Hamiltonian describing the surface states of a toroidal
topological insulator is obtained, and it is shown to support both bound-states
and charged zero-modes. Actually, the spin connection induced by the toroidal
curvature can be viewed as an position-dependent effective vector potential,
which ultimately yields the zero-modes whose wave-functions harmonically
oscillate around the toroidal surface. In addition, two distinct Berry phases
are predicted to take place by the virtue of the toroidal topology.Comment: New version, accepted for publication in EPJB, 6 pages, 1 figur
Ground-state configurations in ferromagnetic nanotori
Magnetization ground states are studied in toroidal nanomagnets. The
energetics associated to the ferromagnetic, vortex and onion-like
configurations are explicitly computed. The analysis reveals that the vortex
appears to be the most prominent of such states, minimizing total energy in
every torus with internal radius (for Permalloy). For
the vortex remains the most favorable pattern whenever
( is the torus external radius and is
the exchange length), being substituted by the ferromagnetic state whenever
.Comment: 16 pages, 9 figures, 3 apendices, Revtex forma
Interaction-free measurements by quantum Zeno stabilisation of ultracold atoms
Quantum mechanics predicts that our physical reality is influenced by events
that can potentially happen but factually do not occur. Interaction-free
measurements (IFMs) exploit this counterintuitive influence to detect the
presence of an object without requiring any interaction with it. Here we
propose and realize an IFM concept based on an unstable many-particle system.
In our experiments, we employ an ultracold gas in an unstable spin
configuration which can undergo a rapid decay. The object - realized by a laser
beam - prevents this decay due to the indirect quantum Zeno effect and thus,
its presence can be detected without interacting with a single atom. Contrary
to existing proposals, our IFM does not require single-particle sources and is
only weakly affected by losses and decoherence. We demonstrate confidence
levels of 90%, well beyond previous optical experiments.Comment: manuscript with 5 figures, 3 supplementary figure, 1 supplementary
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