59 research outputs found
Spin Liquid in the Multiple-Spin Exchange model on the Triangular lattice: 3He on graphite
Using exact diagonalizations, we investigate the T=0 phase diagram of the
Multi-Spin Exchange (MSE) model on the triangular lattice: we find a transition
separating a ferromagnetic phase from a non-magnetic gapped Spin Liquid phase.
Systems far enough from the ferromagnetic transition have a metamagnetic
behavior with magnetization plateaus at m/m_sat=0 and 1/2. The MSE has been
proposed to describe solid 3He films adsorbed onto graphite, thus we compute
the MSE heat capacity for parameters in the low density range of the 2nd layer
and find a double-peak structure.Comment: Revtex, 4 pages, 4 figures. Accepted to Phys. Rev. Let
Comment on "Kagome Lattice Antiferromagnet Stripped to Its Basics"
Density matrix renormalization group (DMRG) calculations on large systems (up
to 3096 spins) indicate that the ground state of the Heisenberg model on a
3-chain Kagome strip is spontaneously dimerized. This system has degenerate
ground states and a gap to triplet and singlet excitations. These results are
in direct contradiction with recent results of Azaria et al (Phys. Rev. Lett.
81, 1694 (1998)) and suggest a need for a reexamination of the underlying field
theory.Comment: 1 page, submitted to PR
The "Square Kagome" Quantum Antiferromagnet and the Eight Vertex Model
We introduce a two dimensional network of corner-sharing triangles with
square lattice symmetry. Properties of magnetic systems here should be similar
to those on the kagome lattice. Focusing on the spin half Heisenberg quantum
antiferromagnet, we generalise the spin symmetry group from SU(2) to SU(N). In
the large N limit, we map the model exactly to the eight vertex model, solved
by Baxter. We predict an exponential number of low-lying singlet states, a
triplet gap, and a two-peak specific heat. In addition, the large N limit
suggests a finite temperature phase transition into a phase with ordered
``resonance loops'' and broken translational symmetry.Comment: 5 pages, revtex, 5 eps figures include
Magneto-thermodynamics of the spin-1/2 Kagome antiferromagnet
In this paper, we use a new hybrid method to compute the thermodynamic
behavior of the spin-1/2 Kagome antiferromagnet under the influence of a large
external magnetic field. We find a T^2 low-temperature behavior and a very low
sensitivity of the specific heat to a strong external magnetic field. We
display clear evidence that this low temperature magneto-thermal effect is
associated to the existence of low-lying fluctuating singlets, but also that
the whole picture (T^2 behavior of Cv and thermally activated spin
susceptibility) implies contribution of both non magnetic and magnetic
excitations. Comparison with experiments is made.Comment: 4 pages, LaTeX 2.09 and RevTeX with 3 figures embedded in the text.
Version to appear in Phys. Rev. Let
Quantum Kagome antiferromagnet ZnCu3(OH)6Cl2
The frustration of antiferromagnetic interactions on the loosely connected
kagome lattice associated to the enhancement of quantum fluctuations for S=1/2
spins was acknowledged long ago as a keypoint to stabilize novel ground states
of magnetic matter. Only very recently, the model compound Herbersmithite,
ZnCu3(OH)6Cl2, a structurally perfect kagome antiferromagnet, could be
synthesized and enables a close comparison to theories. We review and classify
various experimental results obtained over the past years and underline some of
the pending issues.Comment: 23 pages, 16 figures, invited paper in J. Phys. Soc. Jpn, special
topics issue on "Novel States of Matter Induced by Frustration", to be
published in Jan. 201
Ground State and Elementary Excitations of the S=1 Kagome Heisenberg Antiferromagnet
Low energy spectrum of the S=1 kagom\'e Heisenberg antiferromagnet (KHAF) is
studied by means of exact diagonalization and the cluster expansion. The
magnitude of the energy gap of the magnetic excitation is consistent with the
recent experimental observation for \mpynn. In contrast to the KHAF,
the non-magnetic excitations have finite energy gap comparable to the magnetic
excitation. As a physical picture of the ground state, the hexagon singlet
solid state is proposed and verified by variational analysis.Comment: 5 pages, 7 eps figures, 2 tables, Fig. 4 correcte
Numerical-Diagonalization Study of Spin Gap Issue of the Kagome Lattice Heisenberg Antiferromagnet
We study the system size dependence of the singlet-triplet excitation gap in
the kagome-lattice Heisenberg antiferromagnet by numerical
diagonalization. We successfully obtain a new result of a cluster of 42 sites.
The two sequences of gaps of systems with even-number sites and that with
odd-number sites are separately analyzed. Careful examination clarifies that
there is no contradiction when we consider the system to be gapless.Comment: 5 pages, 3 figures, 1 table, received by J. Phys. Soc. Jpn. on 20 Jan
2011, to be published in this journa
The Antiferromagnetic Heisenberg Model on Clusters with Icosahedral Symmetry
The antiferromagnetic Heisenberg model is considered for spins
located on the vertices of the dodecahedron and the icosahedron, which belong
to the point symmetry group . Taking into account the permutational and
spin inversion symmetries of the Hamiltonian results in a drastic reduction of
the dimensionality of the problem, leading to full diagonalization for both
clusters. There is a strong signature of the frustration present in the systems
in the low energy spectrum, where the first excited states are singlets.
Frustration also results in a doubly-peaked specific heat as a function of
temperature for the dodecahedron. Furthermore, there is a discontinuity in the
magnetization as a function of magnetic field for the dodecahedron, where a
specific total spin sector never becomes the ground state in a field. This
discontinuity is accompanied by a magnetization plateau. The calculation is
also extended for where both systems again have singlet excitations.
The magnetization of the dodecahedron has now two discontinuities in an
external field and also magnetization plateaux, and the specific heat of the
icosahedron a two-peak structure as a function of temperature. The similarities
between the two systems suggest that the antiferromagnetic Heisenberg model on
a larger cluster with the same symmetry, the 60-site cluster, will have similar
properties
Residual entropy and spin gap in a one-dimensional analog of the pyrochlore antiferromagnet
We show that the low-energy sector of the S=1/2, antiferromagnetic Heisenberg
model on a one-dimensional lattice of coupled tetrahedra consists of 2^N
replica of the spectrum of the dimerized Heisenberg chain, where N is the
number of tetrahedra.
This provides a proof of the following properties: i) there is a residual
ground-state entropy per spin equal to 2^{1/4}; ii) there is a singlet-triplet
gap as long as the coupling between the tetrahedra is smaller than the internal
one. These properties are compared to available results on the pyrochlore
lattice.Comment: 4 pages with 3 figure
Hidden long range order in Heisenberg Kagome antiferromagnets
We give a physical picture of the low-energy sector of the spin 1/2
Heisenberg Kagome antiferromagnet (KAF). It is shown that Kagome lattice can be
presented as a set of stars which are arranged in a triangular lattice and
contain 12 spins. Each of these stars has two degenerate singlet ground states
which can be considered in terms of pseudospin. As a result of interaction
between stars we get Hamiltonian of the Ising ferromagnet in magnetic field. So
in contrast to the common view there is a long range order in KAF consisting of
definite singlet states of the stars.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
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