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

Practical Use of a Liquid Helium-Free Superconducting Magnet(Magnet Technology)

A cryocooler-cooled 4.6 T superconducting magnet with a 38 mm room temperature bore, which consists of a low-T_c Nb_3Sn coil and high-T_c Bi_2Sr_2Ca_2Cu3O_ current leads, has been working in vacuum for about 18000 cooling hours without trouble, It is found that the high-T_c current leads can hold excellent superconducting properties for a long enough time to be practically used. As a next step, we have succeeded in the construction of a l0.7 T-52 mm room temperature bore and a 5.7 T-220 mm room temperature bore liquid helium-free superconducting magnet

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 %

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

High-Field ESR Measurements of S=1/2 Kagome Lattice Antiferromagnet BaCu3_3V2_2O8_8(OH)2_2

High-field electron spin resonance (ESR) measurements have been performed on vesignieite BaCu$_3$V$_2$O$_8$(OH)$_2$, which is considered as a nearly ideal model substance of $S$=1/2 kagome antiferromagnet, in the temperature region from 1.9 to 265 K. The frequency region is from 60 to 360 GHz and the applied pulsed magnetic field is up to 16 T. Observed g-value and linewidth show the increase below 20 K, which suggest the development of the short range order. Moreover, a gapless spin liquid ground state is suggested from the frequency-field relation at 1.9 K.Comment: 5 pages, 6 figures, jpsj2 class file, to be published in J. Phys. Soc. Jp

Dark-adapted red flash ERGs in healthy adults

Purpose: The x-wave of the dark-adapted (DA) ERG to a red flash reflects DA cone function. This exploratory study of healthy adults aimed to investigate changes in the DA red ERG with flash strength and during dark adaptation to optimise visualisation and therefore quantification of the x-wave. Methods: The effect of altering red flash strength was investigated in four subjects by recording ERGs after 20 minutes dark adaptation to red flashes (0.2–2.0 cd s m-2) using skin electrodes and natural pupils. The effect of dark adaptation duration was investigated in 16 subjects during 20 minutes in the dark, by recording DA 1.5 red ERGs at 1, 2, 3, 4, 5, 10, 15 and 20 minutes. Results: For a dark adaption period of 20 minutes, the x-wave was more clearly visualised to weaker (< 0.6 cd s m-2) red flash strengths: to stronger flashes it became obscured by the b-wave. For red flashes of 1.5 cd s m-2, the x-wave was most prominent in ERGs recorded after 1–5 minutes of dark adaptation: with longer dark-adaptation, it was subsumed into the b-wave’s rising edge. Conclusions: This small study suggests that x-wave visibility in healthy subjects after 20 minutes dark adaptation is improved by using flashes weaker than around 0.6 cd s m-2; for flash strengths of 1.5 cd s m-2, x-wave visibility is enhanced by recording after only around 5 minutes of dark adaptation. No evidence was found that interim red flash ERGs affecting the dark-adapted state of the normal retina

Quantum Fluctuation-Induced Phase Transition in S=1/2 XY-like Heisenberg Antiferromagnets on the Triangular Lattice

The selection of the ground state among nearly degenerate states due to quantum fluctuations is studied for the S=1/2 XY-like Heisenberg antiferromagnets on the triangular lattice in the magnetic field applied along the hard axis, which was first pointed out by Nikuni and Shiba. We find that the selected ground state sensitively depends on the degree of the anisotropy and the magnitude of the magnetic field. This dependence is similar to that in the corresponding classical model at finite temperatures where various types of field induced phases appear due to the entropy effect. It is also found that the similarity of the selected states in the classical and quantum models are not the case in a two-leg ladder lattice, although the lattice consists of triangles locally and the ground state of this lattice in the classical case is the same as that of the triangular lattice.Comment: 15 pages, 35 figure