231 research outputs found
Entanglement Entropy in the Calogero-Sutherland Model
We investigate the entanglement entropy between two subsets of particles in
the ground state of the Calogero-Sutherland model. By using the duality
relations of the Jack symmetric polynomials, we obtain exact expressions for
both the reduced density matrix and the entanglement entropy in the limit of an
infinite number of particles traced out. From these results, we obtain an upper
bound value of the entanglement entropy. This upper bound has a clear
interpretation in terms of fractional exclusion statistics.Comment: 14 pages, 3figures, references adde
Two dimensional modulational instability in photorefractive media
We study theoretically and experimentally the modulational instability of
broad optical beams in photorefractive nonlinear media. We demonstrate the
impact of the anisotropy of the nonlinearity on the growth rate of periodic
perturbations. Our findings are confirmed by experimental measurements in a
strontium barium niobate photorefractive crystal.Comment: 8 figure
Direct observation of nanoscale interface phase in the superconducting chalcogenide KFeSe with intrinsic phase separation
We have used scanning micro x-ray diffraction to characterize different
phases in superconducting KFeSe as a function of temperature,
unveiling the thermal evolution across the superconducting transition
temperature (T32 K), phase separation temperature (T520 K)
and iron-vacancy order temperature (T580 K). In addition to the
iron-vacancy ordered tetragonal magnetic phase and orthorhombic metallic
minority filamentary phase, we have found a clear evidence of the interface
phase with tetragonal symmetry. The metallic phase is surrounded by this
interface phase below 300 K, and is embedded in the insulating texture.
The spatial distribution of coexisting phases as a function of temperature
provides a clear evidence of the formation of protected metallic percolative
paths in the majority texture with large magnetic moment, required for the
electronic coherence for the superconductivity. Furthermore, a clear
reorganization of iron-vacancy order around the T and T is found
with the interface phase being mostly associated with a different iron-vacancy
configuration, that may be important for protecting the percolative
superconductivity in KFeSe.Comment: 6 pages, 4 figure
Nonlinear photonic lattices in anisotropic nonlocal self-focusing media
We analyze theoretically and generate experimentally two-dimensional
nonlinear periodic lattices in a photorefractive medium. We demonstrate that
the light-induced periodically modulated nonlinear refractive index is highly
anisotropic and nonlocal, and it depends on the lattice orientation relative to
the crystal axis. We discuss stability of such induced photonic structures and
their guiding properties.Comment: 3 pages, 3 figure
Induced Coherence and Stable Soliton Spiraling
We develop a theory of soliton spiraling in a bulk nonlinear medium and
reveal a new physical mechanism: periodic power exchange via induced coherence,
which can lead to stable spiraling and the formation of dynamical two-soliton
states. Our theory not only explains earlier observations, but provides a
number of predictions which are also verified experimentally. Finally, we show
theoretically and experimentally that soliton spiraling can be controled by the
degree of mutual initial coherence.Comment: 4 pages, 5 figure
Observation of dipole-mode vector solitons
We report on the first experimental observation of a novel type of optical
vector soliton, a {\em dipole-mode soliton}, recently predicted theoretically.
We show that these vector solitons can be generated in a photorefractive medium
employing two different processes: a phase imprinting, and a symmetry-breaking
instability of a vortex-mode vector soliton. The experimental results display
remarkable agreement with the theory, and confirm the robust nature of these
radially asymmetric two-component solitary waves.Comment: 4 pages, 8 figures; pictures in the PRL version are better qualit
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