590 research outputs found
Itinerant Ferromagnetism in an Atom Trap
We propose an experiment to explore the magnetic phase transitions in
interacting fermionic Hubbard systems, and describe how to obtain the
ferromagnetic phase diagram of itinerant electron systems from these
observations. In addition signatures of ferromagnetic correlations in the
observed ground states are found: for large trap radii (trap radius ,
in units of coherence length ), ground states are topological in nature --
a "skyrmion" in 2D, and a "hedgehog" in 3D.Comment: Final Published version. References adde
Where the Rocks Bleed Ink: Images of Self in Palestinian Political Cartoons
This graphic novel looks at symbols used by three prominent Palestinian political cartoonists—Naji al Ali, Baha Boukhari, and Khalil Abu Arafeh—that represent the Palestinian people. The goal, assuming that political cartoons accurately reflect the opinions of the common people, is to discern what Palestinians think about themselves. This study finds that while the cartoonists use a number of cultural and religious symbols to represent Palestinians, the most regularly used images—and hypothetically the most insightful—are representations of common Palestinian people themselves. They are depicted as humble yet strong and pious. Al Ali’s cartoons are taken from handala.org, a website dedicated to al Ali, his most famous character Handala, and to the Palestinian cause. Boukhari’s and Abu Arafeh’s cartoons come from their personal Facebook pages
Even Parity, Orbital Singlet and Spin Triplet Pairing for Superconducting
In the present paper, we propose the parity even,orbital singlet and spin
triplet pairing state as the ground state of the newly discovered
super-conductor .The pairing mechanism involves both the
special shape of the electron fermi surface and the strong ferromagnetic
fluctuation induced by Hund's rule coupling.The special behavior of the
Bogoliubov quasi-particle spectrum may leads to "Fermi arc" like anisotropy
super-conducting gap, which can be detected by angle resolved photo
emission(ARPES).The impurity effects are also discussed.Comment: 4 pages, 3 figure
Variationnal study of ferromagnetism in the t1-t2 Hubbard chain
A one-dimensional Hubbard model with nearest and (negative) next-nearest
neighbour hopping is studied variationally. This allows to exclude saturated
ferromagnetism for . The variational boundary has a minimum
at a ``critical density'' and diverges for .Comment: 5 pages, LateX and 1 postscript figure. To appear in Physica
Statistical properties of a free-electron laser revealed by the Hanbury Brown and Twiss interferometry
We present a comprehensive experimental analysis of statistical properties of
the self-amplified spontaneous emission (SASE) free-electron laser (FEL) FLASH
at DESY in Hamburg by means of Hanbury Brown and Twiss (HBT) interferometry.
The experiments were performed at the FEL wavelengths of 5.5 nm, 13.4 nm, and
20.8 nm. We determined the 2-nd order intensity correlation function for all
wavelengths and different operation conditions of FLASH. In all experiments a
high degree of spatial coherence (above 50%) was obtained. Our analysis
performed in spatial and spectral domains provided us with the independent
measurements of an average pulse duration of the FEL that were below 60 fs. To
explain complicated behaviour of the 2-nd order intensity correlation function
we developed advanced theoretical model that includes the presence of multiple
beams and external positional jitter of the FEL pulses. By this analysis we
determined that in most experiments several beams were present in radiating
field and in one of the experiments external positional jitter was about 25% of
the beam size. We envision that methods developed in our study will be used
widely for analysis and diagnostics of the FEL radiation.Comment: 29 pages, 14 figures, 3 table
Exact single spin flip for the Hubbard model in
It is shown that the dynamics of a single -electron interacting
with a band of -electrons can be calculated exactly in the limit of
infinite dimension. The corresponding Green function is determined as a
continued fraction. It is used to investigate the stability of saturated
ferromagnetism and the nature of the ground state for two generic non-bipartite
infinite dimensional lattices. Non Fermi liquid behavior is found. For certain
dopings the -electron is bound to the -holes.Comment: 4 pages, 3 figures included with psfig, Revtex; Phys. Rev. Lett. in
press; some amendments made to clarify the calculation of the self-energy,
the extrapolation of the continued fraction, and the statements on
Fermi-liquid theor
Hanbury Brown and Twiss interferometry at a free-electron laser
We present measurements of second- and higher-order intensity correlation
functions (so-called Hanbury Brown and Twiss experiment) performed at the
free-electron laser (FEL) FLASH in the non-linear regime of its operation. We
demonstrate the high transverse coherence properties of the FEL beam with a
degree of transverse coherence of about 80% and degeneracy parameter of the
order 10^9 that makes it similar to laser sources. Intensity correlation
measurements in spatial and frequency domain gave an estimate of the FEL
average pulse duration of 50 fs. Our measurements of the higher-order
correlation functions indicate that FEL radiation obeys Gaussian statistics,
which is characteristic to chaotic sources.Comment: 19 pages, 6 figures, 1 table, 40 reference
Near field wireless power transfer using curved relay resonators for extended transfer distance
Seeded x-ray free-electron laser generating radiation with laser statistical properties
The invention of optical lasers led to a revolution in the field of optics
and even to the creation of completely new fields of research such as quantum
optics. The reason was their unique statistical and coherence properties. The
newly emerging, short-wavelength free-electron lasers (FELs) are sources of
very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse
durations on the order of femtoseconds, and are presently considered to be
laser sources at these energies. Most existing FELs are highly spatially
coherent but in spite of their name, they behave statistically as chaotic
sources. Here, we demonstrate experimentally, by combining Hanbury Brown and
Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI
FEL-2 source does indeed behave statistically as a laser. The first steps have
been taken towards exploiting the first-order coherence of FELs, and the
present work opens the way to quantum optics experiments that strongly rely on
high-order statistical properties of the radiation.Comment: 24 pages, 10 figures, 37 reference
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