212 research outputs found
Magnetic correlations in the S=5/2 quadratic lattice Heisenberg antiferromagnet Mn(HCOO)2ï½¥2(ND2)2CO
The magnetic correlations in the quadratic lattice S=5/2 Heisenberg antiferromagnet Mn(HCOO)2â‹…2(ND2)2CO (TN=3.77K) have been studied by means of specific heat and neutron-scattering experiments. With a universal temperature scale, the temperature behavior of both the magnetic heat capacity and spin correlations are quantitatively accounted for by the pure quantum self-consistent harmonic approximation by Cuccoli et al. for S=5/2
Softening of Magnetic Excitations Leading to Pressure-Induced Quantum Phase Transition in Gapped Spin System KCuCl
KCuCl is a three dimensionally coupled spin dimer system, which undergoes
a pressure-induced quantum phase transition from a gapped ground state to an
antiferromagnetic state at a critical pressure of kbar.
Magnetic excitations in KCuCl at a hydrostatic pressure of 4.7 kbar have
been investigated by conducting neutron inelastic scattering experiments using
a newly designed cylindrical high-pressure clamp cell. A well-defined single
excitation mode is observed. The softening of the excitation mode due to the
applied pressure is clearly observed. From the analysis of the dispersion
relations, it is found that an intradimer interaction decreases under
hydrostatic pressure, while most interdimer interactions increase.Comment: 4 pages, 5 figures, 1 table, jpsj2.cls, to be published in J. Phys.
Soc. Jpn. Vol.76 (2007), the graphic problem of Fig.2 was fixe
Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
The bulk composition of an exoplanet is commonly inferred from its average
density. For small planets, however, the average density is not unique within
the range of compositions. Variations of a number of important planetary
parameters--which are difficult or impossible to constrain from measurements
alone--produce planets with the same average densities but widely varying bulk
compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the
mass of a solid planet causes the radius to increase 5-60% above its gas-free
value. A planet with a given mass and radius might have substantial water ice
content (a so-called ocean planet) or alternatively a large rocky-iron core and
some H and/or He. For example, a wide variety of compositions can explain the
observed radius of GJ 436b, although all models require some H/He. We conclude
that the identification of water worlds based on the mass-radius relationship
alone is impossible unless a significant gas layer can be ruled out by other
means.Comment: 5 pages, 3 figures, accepted to Ap
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
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