173 research outputs found
H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH)CHNHCu(ClBr)
Spin-lattice relaxation rate of H-NMR has been measured in
(CH)CHNHCu(ClBr) with , which has been
reported to be gapped system with singlet ground state from the previous
macroscopic magnetization and specific heat measurements, in order to
investigate the bond randomness effect microscopically in the gapped composite
Haldane system (CH)CHNHCuCl. It was found that the spin-lattice
relaxation rate in the present system includes both fast and slow
relaxation parts indicative of the gapless magnetic ground state and the gapped
singlet ground state, respectively. We discuss the obtained results with the
previous macroscopic magnetization and specific heat measurements together with
the microscopic SR experiments.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. vol.76
(2007) No.
Dynamics of composite Haldane spin chains in IPA-CuCl3
Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl3
are studied by cold neutron inelastic scattering. Strongly dispersive gap
excitations are observed. Contrary to previously proposed models, the system is
best described as an asymmetric quantum spin ladder. The observed spectrum is
interpreted in terms of ``composite'' Haldane spin chains. The key difference
from actual S=1 chains is a sharp cutoff of the single-magnon spectrum at a
certain critical wave vector.Comment: 4 pages 4 figure
Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders
The weakly coupled quasi-one-dimensional spin ladder compound
(CH)CHNHCuCl is studied by neutron scattering in magnetic
fields exceeding the critical field of Bose-Einstein condensation of magnons.
Commensurate long-range order and the associated Goldstone mode are detected
and found to be similar to those in a reference 3D quantum magnet. However, for
the upper two massive magnon branches the observed behavior is totally
different, culminating in a drastic collapse of excitation bandwidth beyond the
transition point.Comment: 4 pages, 4 figure
Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain as a model system for Cu(3-Clpy)(N)
Thermodynamic properties of a tetramer
ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain
are investigated by the use of an exact mapping transformation technique. Exact
results for the magnetization, susceptibility and specific heat in the zero as
well as nonzero magnetic field are presented and discussed in detail. The
results obtained from the mapping are compared with the relevant experimental
data of Cu(3-Clpy)(N) (3-Clpy=3-Chloropyridine).Comment: 10 pages, 1 table, 14 figures, to be presented at CSMAG04 conferenc
Neutron Scattering Study of Magnetic Ordering and Excitations in the Doped Spin Gap System Tl(CuMg)Cl
Neutron elastic and inelastic scattering measurements have been performed in
order to investigate the spin structure and the magnetic excitations in the
impurity-induced antiferromagnetic ordered phase of the doped spin gap system
Tl(CuMg)Cl with . The magnetic Bragg reflections
indicative of the ordering were observed at with integer
and odd below K. It was found that the spin structure
of the impurity-induced antiferromagnetic ordered phase on average in
Tl(CuMg)Cl with is the same as that of the
field-induced magnetic ordered phase for in the parent
compound TlCuCl. The triplet magnetic excitation was clearly observed in
the - plane and the dispersion relations of the triplet excitation
were determined along four different directions. The lowest triplet excitation
corresponding to the spin gap was observed at with integer
and odd , as observed in TlCuCl. It was also found that the spin gap
increases steeply below upon decreasing temperature. This strongly
indicates that the impurity-induced antiferromagnetic ordering coexists with
the spin gap state in Tl(CuMg)Cl with .Comment: 24 pages, 7 figures, 11 eps files, revtex style, will appear in Phys.
Rev.
Efimov effect in quantum magnets
Physics is said to be universal when it emerges regardless of the underlying
microscopic details. A prominent example is the Efimov effect, which predicts
the emergence of an infinite tower of three-body bound states obeying discrete
scale invariance when the particles interact resonantly. Because of its
universality and peculiarity, the Efimov effect has been the subject of
extensive research in chemical, atomic, nuclear and particle physics for
decades. Here we employ an anisotropic Heisenberg model to show that collective
excitations in quantum magnets (magnons) also exhibit the Efimov effect. We
locate anisotropy-induced two-magnon resonances, compute binding energies of
three magnons and find that they fit into the universal scaling law. We propose
several approaches to experimentally realize the Efimov effect in quantum
magnets, where the emergent Efimov states of magnons can be observed with
commonly used spectroscopic measurements. Our study thus opens up new avenues
for universal few-body physics in condensed matter systems.Comment: 7 pages, 5 figures; published versio
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