369 research outputs found
Temperature dependence of single particle excitations in a S=1 chain: exact diagonalization calculations compared to neutron scattering experiments
Exact diagonalization calculations of finite antiferromagnetic spin-1
Heisenberg chains at finite temperatures are presented and compared to a recent
inelastic neutron scattering experiment for temperatures T up to 7.5 times the
intrachain exchange constant J. The calculations show that the excitations at
the antiferromagnetic point q=1 and at q=0.5 remain resonant up to at least
T=2J, confirming the recent experimental observation of resonant
high-temperature domain wall excitations. The predicted first and second
moments are in good agreement with experiment, except at temperatures where
three-dimensional spin correlations are most important. The ratio of the
structure factors at q=1 and at q=0.5 is well predicted for the paramagnetic
infinite-temperature limit. For T=2J, however, we found that the experimentally
observed intensity is considerably less than predicted. This suggests that
domain wall excitations on different chains interact up to temperatures of the
order of the spin band width.Comment: 9 pages revtex, submitted to PR
Substantially enhanced cloning efficiency of SAGE (Serial Analysis of Gene Expression) by adding a heating step to the original protocol
The efficiency of the original SAGE (Serial Analysis of Gene Expression) protocol was limited by a small average size of cloned concatemers. We describe a modification of the technique that overcomes this problem. Ligation of ditags yields concatemers of various sizes. Small concatemers may aggregate and migrate with large ones during gel electrophoresis. A heating step introduced before gel electrophoresis breaks such contaminating aggregates. This modification yields cloned concatemers with an average size of 67 tags as compared to 22 tags by the original protocol. It enhances the length of cloned concatemers substantially and reduces the costs of SAG
Temperature Evolution of the Quantum Gap in CsNiCl3
Neutron scattering measurements on the one-dimensional gapped S=1
antiferromagnet, CsNiCl3, have shown that the excitation corresponding to the
Haldane mass gap Delta at low temperatures persists as a resonant feature to
high temperatures. We find that the strong upward renormalisation of the gap
excitation, by a factor of three between 5 and 70K, is more than enough to
overcome its decreasing lifetime. We find that the gap lifetime is
substantially shorter than that predicted by the scaling theory of Damle and
Sachdev in its low temperature range of validity. The upward gap
renormalisation agrees with the non-linear sigma model at low temperatures and
even up to T of order 2Delta provided an upper mass cutoff is included.Comment: Latex, 3 figures, accepted by Pysical Review
Comment on Ferroelectricity in Spiral Magnets
A Comment on the Letter by Maxim Mostovoy, [Phys. Rev. Lett. 96, 067601 (2006)]. The author of the Letter offers a Reply
Magnetically-induced electric polarization in an organo-metallic magnet
The coupling between magnetic order and ferroelectricity has been under
intense investigation in a wide range of transition-metal oxides. The strongest
coupling is obtained in so-called magnetically-induced multiferroics where
ferroelectricity arises directly from magnetic order that breaks inversion
symmetry. However, it has been difficult to find non-oxide based materials in
which these effects occur. Here we present a study of copper dimethyl sulfoxide
dichloride (CDC), an organo-metallic quantum magnet containing Cu
spins, in which electric polarization arises from non-collinear magnetic order.
We show that the electric polarization can be switched in a stunning hysteretic
fashion. Because the magnetic order in CDC is mediated by large organic
molecules, our study shows that magnetoelectric interactions can exist in this
important class of materials, opening the road to designing magnetoelectrics
and multiferroics using large molecules as building blocks. Further, we
demonstrate that CDC undergoes a magnetoelectric quantum phase transition where
both ferroelectric and magnetic order emerge simultaneously as a function of
magnetic field at very low temperatures
Magnetic Order and Spin Dynamics in Ferroelectric HoMnO
Hexagonal HoMnO is a frustrated antiferromagnet (T=72 K)
ferroelectric (T=875 K) in which these two order parameters are coupled.
Our neutron measurements of the spin wave dispersion for the S=2 Mn on
the layered triangular lattice are well described by a two-dimensional
nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy that is
0.093 meV above the spin reorientation transition at 40 K, and 0.126 meV below.
For the magnetic structures and phase diagram have been
determined, and reveal additional transitions below 8 K where the
ferroelectrically displaced Ho ions are ordered magnetically.Comment: To be published in Physical Review Letter
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