473 research outputs found
The Project for the New High Field Facility
Since High Field Laboratory for Superconducting Materials attached to Institute for Materials Research of Tohoku University started, 15 years has passed. We have had plenty of fruitful scientific and technological results not only in a field of superconductivity but also in areas of magnetism, semiconductors, organic conductors, chemical and biological materials and crystallography. The equipments in the Laboratory, however, are now getting aged and the available high field of 31 T obtained by our hybrid magnet, which used to be the highest in the world, must be graded up. The committee of the Laboratory has been discussing on the development of equipments and expansion of research fields for the new facility
Theory of phonon-assisted "forbidden" optical transitions in spin-gapped systems
We consider the absorption of light with emission of one S(tot)=1 magnetic
excitation in systems with a spin gap induced by quantum fluctuations. We argue
that an electric dipole transition is allowed on the condition that a virtual
phonon instantaneously breaks the inversion symmetry. We derive an effective
operator for the transition and argue that the proposed theory explains the
polarized experiments in CuGeO(3) and SrCu(2)[BO(3)](2).Comment: 9 pages, 4 figure
Coherent radiation by molecular magnets
The possibility of coherent radiation by molecular magnets is investigated.
It is shown that to realize the coherent radiation, it is necessary to couple
the considered sample to a resonant electric circuit. A theory for describing
this phenomenon is developed, based on a realistic microscopic Hamiltonian,
including the Zeeman terms, single-site anisotropy, and dipole interactions.
The role of hyperfine interactions between molecular and nuclear spins is
studied. Numerical solutions of the spin evolution equations are presented.Comment: Latex file, 11 pages, 3 figure
ESR investigation on the Breather mode and the Spinon-Breather dynamical crossover in Cu Benzoate
A new elementary-excitation, the so called "breather excitation", is observed
directly by millimeter-submillimeter wave electron spin resonance (ESR) in the
Heisenberg quantum spin-chain Cu benzoate, in which a field-induced gap is
found recently by specific heat and neutron scattering measurements. Distinct
anomalies were found in line width and in resonance field around the "dynamical
crossover" regime between the gap-less spinon-regime and the gapped
breather-regime. When the temperature becomes sufficiently lower than the
energy gap, a new ESR-line with very narrow line-width is found, which is the
manifestation of the breather excitation. The non-linear field dependence of
the resonance field agrees well with the theoretical formula of the first
breather-excitation proposed by Oshikawa and Affleck. The present work
establishes experimentally for the first time that a sine-Gordon model is
applicable to explain spin dynamics in a S=1/2 Heisenberg spin chain subjected
to staggered field even in high fields.Comment: Revtex, 4 pages, 4 figures, submitted to Phys. Rev. Let
Magnetic structures of RbCuCl_3 in a transverse field
A recent high-field magnetization experiment found a phase transition of
unknown character in the layered, frustrated antiferromagnet RbCuCl_3, in a
transverse field (in the layers). Motivated by these results, we have examined
the magnetic structures predicted by a model of RbCuCl_3, using the classical
approximation. At small fields, we obtain the structure already known to be
optimal, an incommensurate (IC) spiral with wave vector q in the layers. At
higher fields, we find a staircase of long-period commensurate (C) phases
(separated initially by the low-field IC phase), then two narrow IC phases,
then a fourth IC phase (also with intermediate C phases), and finally the
ferromagnetically aligned phase at the saturation field H_S. The
three-sublattice C states familiar from the theory of the triangular
antiferromagnet are never optimal. The C phases and the two intermediate IC
phases were previously unknown in this context. The magnetization is
discontinuous at a field \approx 0.4H_S, in qualitative agreement with
experiment, though we find much fine structure not reported.Comment: 9 pages, 8 figure
Highly Strengthened Superconducting Magnet for a 40 T Compact Hybrid Magnet(Magnet Technology)
A 16 T outer superconducting magnet for a 40 T compact hybrid magnet is investigated. A highly strengthened superconducting magnet with a 360 mm room temperature bore can be made using newly developed (Nb, Ti)_3Sn wires with Cu-Al_2O_3 reinforcing stabilizer. The coil weight is outstandingly reduced by as much as 70 %
- …