4,752 research outputs found
Multi-Triplet Magnons in SrCu(BO) Studied by Thermal Conductivity Measurements in Magnetic Fields
We have measured the thermal conductivity parallel to the a-axis of the
Zn-free and 1% Zn-substituted SrCuZn(BO) in magnetic fields
up to 14 T, in order to examine the thermal conductivity due to the
multi-triplet magnons. It has been found that the thermal conductivity peak
observed in the spin gap state is suppressed by the substitution of Zn for Cu
in high magnetic fields above 6 T, while it is not changed in low magnetic
fields below 6 T. The results suggest that the thermal conductivity peak in the
spin-gap state of SrCu(BO) is composed of not only thermal
conductivity due to phonons but also that due to the multi-triplet magnons in
high fields above 6 T.Comment: 7 pages, 2 figure
Doubly excited ferromagnetic spin-chain as a pair of coupled kicked rotors
We show that the dynamics of a doubly-excited 1D Heisenberg ferromagnetic
chain, subject to short pulses from a parabolic magnetic field may be analyzed
as a pair of quantum kicked rotors. By focusing on the two-magnon dynamics in
the kicked XXZ model we investigate how the anisotropy parameter - which
controls the strength of the magnon-magnon interaction - changes the nature of
the coupling between the two "image" coupled Kicked Rotors. We investigate
quantum state transfer possibilities and show that one may control whether the
spin excitations are transmitted together, or separate from each other.Comment: 8 pages, 4 figures; extended appendix and corrected typo
Lyot-based Low Order Wavefront Sensor: Implementation on the Subaru Coronagraphic Extreme Adaptive Optics System and its Laboratory Performance
High throughput, low inner working angle (IWA) phase masks coronagraphs are
essential to directly image and characterize (via spectroscopy) earth-like
planets. However, the performance of low-IWA coronagraphs is limited by
residual pointing errors and other low-order modes. The extent to which
wavefront aberrations upstream of the coronagraph are corrected and calibrated
drives coronagraphic performance. Addressing this issue is essential for
preventing coronagraphic leaks, thus we have developed a Lyot-based low order
wave front sensor (LLOWFS) to control the wavefront aberrations in a
coronagraph. The LLOWFS monitors the starlight rejected by the coronagraphic
mask using a reflective Lyot stop in the downstream pupil plane. The early
implementation of LLOWFS at LESIA, Observatoire de Paris demonstrated an open
loop measurement accuracy of 0.01 lambda/D for tip-tilt at 638 nm when used in
conjunction with a four quadrant phase mask (FQPM) in the laboratory. To
further demonstrate our concept, we have installed the reflective Lyot stops on
the Subaru Coronagraphic Extreme AO (SCExAO) system at the Subaru Telescope and
modified the system to support small IWA phase mask coronagraphs (< 1 lambda/D)
on-sky such as FQPM, eight octant phase mask, vector vortex coronagraph and the
phase induced amplitude apodization complex phase mask coronagraph with a goal
of obtaining milli arc-second pointing accuracy. Laboratory results have shown
the measurement of tip, tilt, focus, oblique and right astigmatism at 1.55 um
for the vector vortex coronagraph. Our initial on-sky result demonstrate the
closed loop accuracy of < 7 x 10-3 lambda/D at 1.6 um for tip, tilt and focus
aberrations with the vector vortex coronagraph.Comment: 9 pages, 9 Figures, Proc. of SPIE Astronomical Telescopes +
Instrumentation 201
Effective optical identification of type "0-IIb" early gastric cancer with narrow band imaging magnification endoscopy, successfully treated by endoscopic submucosal dissection
Background Endoscopic submucosal dissection (ESD) is currently considered the minimal invasive endoscopic treatment for early gastric cancer. Most superficial gastric neoplastic lesions are depressed type â0-IIcâ (70-80%), while totally flat, classified as type â0-IIbâ early gastric cancer, is rarely reported (0.4%). The aim of the present study was to assess the efficacy of narrow band imaging (NBI) magnification endoscopy in identifying type â0-IIbâ early gastric cancer and ESD treatment with curative intention.Methods Twelve of 615 (2%) patients (10 males, median 72 years), treated by ESD at our center, were diagnosed as type â0-IIbâ gastric cancer. Ten had exclusively type â0-IIbâ, while two had combined types â0-IIb+IIcâ and â0-IIa+IIbâ gastric cancer. Initial diagnosis was made during screening gastroscopy, while NBI magnification endoscopy combined with indigo-carmine chromoendoscopy were also used.Results White light endoscopy showed only superficial redness. One patient with signet-ring carcinoma showed whitish appearance. Indigo-carmine chromoendoscopy showed better visualization, while NBI magnification endoscopy revealed abnormal mucosal microsurface and microvascular findings which enabled border marking. ESD with curative intention was completed without complications. Histological examination showed complete (R0) resection, in 10 patients (83%). One patient with positive margins received additional surgery (8%). Mean procedure time was 149 (range 60-190) min. One to six years post-ESD all patients remain alive.Conclusions ESD is considered a safe and effective curative treatment for type â0-IIbâ gastric cancer, resulting in long-term disease-free survival. NBI magnification endoscopy is effective for accurate optical identification and border marking of type â0-IIbâ early gastric cancer
Level statistics of XXZ spin chains with a random magnetic field
The level-spacing distribution of a spin 1/2 XXZ chain is numerically studied
under random magnetic field. We show explicitly how the level statistics
depends on the lattice size L, the anisotropy parameter , and the mean
amplitude of the random magnetic field h. In the energy spectrum, quantum
integrability competes with nonintegrability derived from the randomness, where
the XXZ interaction is modified by the parameter . When ,
the level-spacing distribution mostly shows Wigner-like behavior, while when
=0, Poisson-like behavior appears although the system is nonintegrable
due to randomness. Poisson-like behavior also appears for in the
large h limit. Furthermore, the level-spacing distribution depends on the
lattice size L, particularly when the random field is weak.Comment: 4 pages, 3 figures, to be published in Phys. Rev.
Unexpected non-Wigner behavior in level-spacing distributions of next-nearest-neighbor coupled XXZ spin chains
The level-spacing distributions of XXZ spin chains with next-nearest-neighbor
couplings are studied under periodic boundary conditions. We confirm that
integrable XXZ spin chains mostly have the Poisson distribution as expected. On
the contrary, the level-spacing distributions of next-nearest-neighbor coupled
XXZ chains are given by non-Wigner distributions. It is against the
expectations, since the models are nonintegrable.Comment: 4 pages, 4 figures, to be published in Physical Review
Enhancement of the Thermal Conductivity in gapped Quantum Spin Chains
We study mechanism of magnetic energy transport, motivated by recent
measurements of the thermal conductivity in low dimensional quantum magnets. We
point out a possible mechanism of enhancement of the thermal conductivity in
gapped magnetic system, where the magnetic energy transport plays a crucial
role. This mechanism gives an interpretation for the recent experiment of
CuGeO_3, where the thermal conductivity depends on the crystal direction.Comment: 4 pages, 2 figure
Candidate local parent Hamiltonian for 3/7 fractional quantum Hall effect
While a parent Hamiltonian for Laughlin wave function has been long
known in terms of the Haldane pseudopotentials, no parent Hamiltonians are
known for the lowest-Landau-level projected wave functions of the composite
fermion theory at with . If one takes the two lowest Landau
levels to be degenerate, the Trugman-Kivelson interaction produces the
unprojected 2/5 wave function as the unique zero energy solution. If the lowest
three Landau levels are assumed to be degenerate, the Trugman-Kivelson
interaction produces a large number of zero energy states at . We
propose that adding an appropriately constructed three-body interaction yields
the unprojected wave function as the unique zero energy solution, and
report extensive exact diagonalization studies that provide strong support to
this proposal.Comment: 11 pages, 2 figure
Exactly Solvable Hamiltonian for Non-Abelian Quasiparticles
Particles obeying non-Abelian braid statistics have been predicted to emerge
in the fractional quantum Hall effect. In particular, a model Hamiltonian with
short-range three-body interaction () between electrons
confined to the lowest Landau level provides exact solutions for quasiholes,
and thereby allows a proof of principle for the existence of quasiholes obeying
non-Abelian braid statistics. We construct, in terms of two- and three- body
Haldane pseudopotentials, a model Hamiltonian that can be solved exactly for
both quasiholes and quasiparticles, and provide evidence of non-Abelian
statistics for the latter as well. The structure of the quasiparticle states of
this model is in agreement with that predicted by the bipartite
composite-fermion model of quasiparticles with exact lowest Landau level
projection. We further demonstrate adiabatic continuity for the ground state,
the ordinary neutral excitation, and the topological exciton as we deform our
model Hamiltonian continuously into the lowest Landau-level
Hamiltonian.Comment: 15 pages, 10 figure
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