230 research outputs found
A class of Heisenberg models with the orthogonal dimer ground states
Extensions of the Shastry-Sutherland model are possible in various ways. In
particular, it is possible to construct a natural model in three dimensions
which has the exact dimer ground state. Recently found spin gap system
SrCu_2(BO_3)_2 has this structure. The exchange constants between the layers is
expected to be smaller than the intra-layer couplings. However, the exactness
of the dimer state for the three dimensional structure is important to
understand why magnetic properties of SrCu_2(BO_3)_2 are described well by the
two dimensional model.Comment: 3 pages, 5 figures, to appear in Journal of Physics: Condensed Matte
Theory of absorption in a frustrated spin gap system
We achieve a comprehensive understanding of the magnetic excitations observed
by electric spin resonance and far-infrared spectroscopy in a frustrated spin
gap system by considering the effects of magnetoelectric
couplings and Dzyaloshinskii-Moriya interactions in the Shastry-Sutherland
model. The transitions from the dimer singlet ground state to the triplon and
the bound states of two triplons are electroactive through the magnetoelectric
couplings, even in the Shastry-Sutherland Heisenberg model. The results
indicate that an electro-triplon and a novel electroactive magnetic excitation,
as with an electromagnon in the multiferroics, can be realized in the
conventional spin-gapped singlet and anomalous spin-liquid states. Clarifying
these electroactive magnetic excitations in various spin systems will help
analyze a broad range of quantum magnets, {\it e.g.}, quantum spin liquids and
spin nematics.Comment: 6 pages, 6 figure
Ising phases of Heisenberg ladders in a magnetic field
We examine the influence of weak anisotropic interactions on the T=0 phase
diagram of the frustrated two-leg Heisenberg ladder, a well-studied spin model
exhibiting integer and fractional magnetization plateaux separated by gapless
incommensurate states. We find that the Dzyaloshinskii--Moriya coupling may
substantially modify the phase diagram so that the half-integer plateau and the
surrounding gapless phases merge into a single Ising-ordered phase breaking the
translational symmetry of the lattice. A different Ising order is found for a
weakly frustrated ladder. Implications for experimental ladder and dimer
systems are discussed.Comment: 5 pages, 5 figure
Petrography of Yamato 984028 lherzolitic shergottite and its melt vein: Implications for its shock metamorphism and origin of the vein
AbstractYamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories
Two- and three dimensional frustrated spin systems(New Developments in Strongly Correlated Electron Systems)
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