1,849 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
Low-Lying Magnetic Excitation of the Shastry-Sutherland Model
By using perturbation calculation and numerical diagonalization, low-energy
spin dynamics of the Shastry-Sutherland model is investigated paying particular
attention to the two-particle coherent motion. In addition to spin-singlet- and
triplet bound states, we find novel branches of coherent motion of a bound
quintet pair, which are usually unstable because of repulsion. Unusual
dispersion observed in neutron-scattering measurements are explained by the
present theory. The importance of the effects of phonon is also pointed out.Comment: 4 pages, 6 figures combined into 1 PSfile. Final version to appear in
Phys.Rev.Lett. (Jan. 2000
Magnon Dispersion and Anisotropies in SrCu(BO)
We study the dispersion of the magnons (triplet states) in
SrCu(BO) including all symmetry-allowed Dzyaloshinskii-Moriya
interactions. We can reduce the complexity of the general Hamiltonian to a new
simpler form by appropriate rotations of the spin operators. The resulting
Hamiltonian is studied by both perturbation theory and exact numerical
diagonalization on a 32-site cluster. We argue that the dispersion is dominated
by Dzyaloshinskii-Moriya interactions. We point out which combinations of these
anisotropies affect the dispersion to linear-order, and extract their
magnitudes.Comment: 11 pages, 7 figures, 1 table, v2 conclusion shortened, figs clarifie
Strong coupling theory of the spinless charges on the triangular lattices: possibility of a new quantum liquid
We propose a new type of charge liquid state in the spinless fermion system
on a triangular lattice under strong inter-site Coulomb interactions, . In
the strong coupling limit (), the ground state is classical and disordered
due to geometrical frustration. The introduction of small t will drive the
system to a partially ordered phase which we call a "pinball liquid". A
possibly long range ordered Wigner crystal solid coexist with a liquid
component which are moving around them like a pinball. This liquid is dominant
over wide range of filling, even away from the regular triangle, and is also
realized in the hard core boson systems. Relevance to the organic theta-ET_2X
is discsussed.Comment: 4pages, 7figure
Ferroelectricity induced by spin-dependent metal-ligand hybridization in BaCoGeO
We have investigated the variation of induced ferroelectric polarization
under magnetic field with various directions and magnitudes in a staggered
antiferromagnet BaCoGeO. While the ferroelectric polarization
cannot be explained by the well-accepted spin current model nor exchange
striction mechanism, we have shown that it is induced by the spin-dependent
- hybridization between the transition-metal (Co) and ligand (O) via the
spin-orbit interaction. On the basis of the correspondence between the
direction of electric polarization and the magnetic state, we have also
demonstrated the electrical control of the magnetization direction.Comment: 4 pages, 4 figure
Field-Induced Effects of Anisotropic Magnetic Interactions in SrCu2(BO3)2
We observed a field-induced staggered magnetization in the 2D frustrated
dimer-singlet spin system SrCu2(BO3)2 by 11B NMR, from which the magnitudes of
the intradimer Dzyaloshinsky-Moriya interaction and the staggered g-tensor were
determined. These anisotropic interactions cause singlet-triplet mixing and
eliminate a quantum phase transition at the expected critical field Hc for gap
closing. They also provide a quantitative account for some puzzling phenomena
such as the onset of a uniform magnetization below the and the persistence of
the excitation gap above Hc. The gap was accurately determined from the
activation energy of the nuclear relaxation rate.Comment: 8 pages, 5 figures, published versio
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