7,990 research outputs found
Crystalline Electric Field and Kondo Effect in SmOs4Sb12
Our ultrasound results obtained in pulsed magnetic fields show that the
filled-skutterudite compound SmOsSb has the quartet
crystalline-electric-field ground state. This fact suggests that the multipolar
degrees of freedom of the quartet play an important role in the
unusual physical properties of this material. On the other hand, the elastic
response below 20 T cannot be explained using the localized
4-electron model, which does not take into account the Kondo effect or
ferromagnetic ordering. The analysis result suggests the presence of a
Kondo-like screened state at low magnetic fields and its suppression at high
magnetic fields above 20 T even at low temperatures.Comment: 4 pages, 4 figure
Universal properties of highly frustrated quantum magnets in strong magnetic fields
The purpose of the present paper is two-fold. On the one hand, we review some
recent studies on the low-temperature strong-field thermodynamic properties of
frustrated quantum spin antiferromagnets which admit the so-called
localized-magnon eigenstates. One the other hand, we provide some complementary
new results. We focus on the linear independence of the localized-magnon
states, the estimation of their degeneracy with the help of auxiliary classical
lattice-gas models and the analysis of the contribution of these states to
thermodynamics.Comment: Paper based on the invited talk given by J. Richter at the
International Conference "Statistical Physics 2006. Condensed Matter: Theory
and Applications" dedicated to the 90th anniversary of Ilya Lifshitz
(Kharkiv, 11-15 September, 2006
Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12
Elastic properties of the filled skutterudite compound SmOsSb have
been investigated by ultrasonic measurements. The elastic constant
shows two ultrasonic dispersions at 15 K and 53 K
for frequencies between 33 and 316 MHz, which follow a Debye-type
formula with Arrhenius-type temperature-dependent relaxation times, and remain
unchanged even with applied magnetic fields up to 10 T. The corresponding
activation energies were estimated to be = 105 K and = 409 K,
respectively. The latter, , is the highest value reported so far in the
Sb-based filled skutterudites. The presence of magnetically robust ultrasonic
dispersions in SmOsSb implies a possibility that an emergence of a
magnetically insensitive heavy fermion state in this system is associated with
a novel local charge degree of freedom which causes the ultrasonic dispersion.Comment: 5 pages, 4 figure
Toward Identification of Order Parameters in Skutterudites - a Wonderland of Strong Correlation Physics -
Current status is described toward identifying unconventional order
parameters in filled skutterudites with unique ordering phenomena. The order
parameters in PrFeP and PrRuP are discussed in relation
to associated crystalline electric field (CEF) states and angular form factors.
By phenomenological Landau analysis, it is shown that a scalar order model
explains most properties in both PrFeP and PrRuP with
very different magnetic properties. In particular, the highly anisotropic
susceptibility induced by uniaxial pressure in PrFeP is explained in
terms of two types of couplings. In the case of SmRuP, the main
order parameter at low field is identified as magnetic octupoles. A microscopic
mechanism is proposed how the dipole and octupole degrees of freedom mix under
the point group of skutterudites.Comment: To be published in Proc. International Conference on New Quantum
Phenomena in Skutterudite and Related Systems (Suppl. J. Phys. Soc. Jpn 78,
2008
Asymmetric synthesis of gonytolide A: strategic use of an aryl halide blocking group for oxidative coupling
The first synthesis of the chromanone lactone dimer gonytolide A has been achieved employing vanadium(V)-mediated oxidative coupling of the monomer gonytolide C. An o-bromine blocking group strategy was employed to favor para- para coupling and to enable kinetic resolution of (±)-gonytolide C. Asymmetric conjugate reduction enabled practical kinetic resolution of a chiral, racemic precursor and the asymmetric synthesis of (+)-gonytolide A and its atropisomer.We thank the National Institutes of Health (R35 GM-118173) for research support. Work at the BU-CMD is supported by NIH R24 Grant GM-111625. We thank Prof. Scott Miller and Dr. Anthony Metrano (Yale University) for helpful discussions and preliminary experiments. We thank the Uehara Memorial Foundation for a postdoctoral fellowship to T.I., the American Cancer Society for a postdoctoral fellowship to K.D.R. (PF-16-235-01-CDD), Dr. Jeffrey Bacon (Boston University) for X-ray crystal structure analyses, and Prof. Haruhisa Kikuchi (Tohoku University) for providing a natural sample of gonytolide A. NMR (CHE-0619339) and MS (CHE-0443618) facilities at Boston University are supported by the NSF. (R35 GM-118173 - National Institutes of Health; GM-111625 - NIH; Uehara Memorial Foundation; PF-16-235-01-CDD - American Cancer Society; CHE-0619339 - NSF; CHE-0443618 - NSF
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