274 research outputs found
Changes in the C-type Natriuretic peptide (CNP) and NO derivatives in the plasma and CSF of the patients with subarachnoid hemorrhage (SAH)
Efficacy of the endotoxin absorption method (PMX) in patients with septic shock associated with intraperitoneal infections
Changes in C-type natriuretic peptide (CNP) levels in the plasma and cerebrospinal fluid of the patients with subarachnoid hemorrhage
Instability of isolated triplet excitations on the Shastry-Sutherland lattice (SSL)
Configurations of singlets and triplets on the SSL have been proposed in the
literature as variational ground states of the Shastry-Sutherland model at
fixed magnetization M. We prove, that isolated triplet excitations on the SSL
are unstable if the coupling alpha falls below a critical value alpha_c=2.0
(approx.). The instability should be visible in the compound SrCu_2(BO_3)_2
where a coupling alpha^*=1.48 is realized.Comment: 4 pages, 4 figures, RevTe
Far infrared study of the two dimensional dimer spin system SrCu_2(BO_3)_2
Using far-infrared spectroscopy in magnetic fields up to 12T we have studied
a two-dimensional dimer spin gap system SrCu_2(BO_3)_2. We found several
infrared active modes in the dimerized state (below 10K) in the frequency range
from 3 to 100cm^-1. The measured splitting from the ground state to the excited
triplet M_S=0 sublevel is Delta_1=24.2cm^-1 and the other two triplet state
sublevels in zero magnetic field are 1.4cm^-1 below and above the M_S=0
sublevel. Another multiplet is at Delta_2=37.6cm^-1 from the ground state. A
strong electric dipole active transition polarized in the (ab)-plane is
activated in the dimer spin system below 15K at 52cm^-1.Comment: 4 pages including 5 figures, submitted to PRB, instrumental arte
facts remove
Numerical Study of Excited States in the Shastry-Sutherland Model
We investigate excited states of the Shastry-Sutherland model using a kind of
variational method. Starting from various trial states which include one or two
triplet dimers, we numerically pursue the best evaluation of the energy for
each set of quantum numbers. We present the energy difference as a function of
either the coupling ratio or the momentum and compare them with the
perturbative calculations. Our data suggest that the helical order phase exists
between the singlet dimer phase and the magnetically ordered phase. In
comparison with the experimental data we can estimate the intra-dimer coupling
J and the inter-dimer coupling J' for
SrCu2(BO3)2 : J'/J =0.65 and J = 87K.Comment: 15pages, 5figures to be published in JPS
Low-Lying Magnetic Excitation of the Shastry-Sutherland Model
By using perturbation calculation and numerical diagonalization, low-energy
spin dynamics of the Shastry-Sutherland model is investigated paying particular
attention to the two-particle coherent motion. In addition to spin-singlet- and
triplet bound states, we find novel branches of coherent motion of a bound
quintet pair, which are usually unstable because of repulsion. Unusual
dispersion observed in neutron-scattering measurements are explained by the
present theory. The importance of the effects of phonon is also pointed out.Comment: 4 pages, 6 figures combined into 1 PSfile. Final version to appear in
Phys.Rev.Lett. (Jan. 2000
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