1,194 research outputs found
Precise estimation of the S = 2 Haldane gap by numerical diagonalization
The Haldane gap of the S=2 Heisenberg antiferromagnet in a one-dimensional
linear chain is examined by a numerical-diagonalization method. A precise
estimate for the magnitude of the gap is successfully obtained by a multistep
convergence-acceleration procedure applied to finite-size diagonalization data
under the twisted boundary condition.Comment: 6 pages, 1 Table, to be published in J. Phys. Soc. Jp
Magnetization Process of the Spin-1/2 Triangular-Lattice Heisenberg Antiferromagnet with Next-Nearest-Neighbor Interactions -- Plateau or Nonplateau
An triangular-lattice Heisenberg antiferromagnet with
next-nearest-neighbor interactions is investigated under a magnetic field by
the numerical-diagonalization method. It is known that, in both cases of weak
and strong next-nearest-neighbor interactions, this system reveals a
magnetization plateau at one-third of the saturated magnetization. We examine
the stability of this magnetization plateau when the amplitude of
next-nearest-neighbor interactions is varied. We find that a nonplateau region
appears between the plateau phases in the cases of weak and strong
next-nearest-neighbor interactions.Comment: 6pages, 7figures, to be published in J. Phys. Soc. Jp
Ferrimagnetism in the Spin-1/2 Heisenberg Antiferromagnet on a Distorted Triangular Lattice
The ground state of the spin- Heisenberg antiferromagnet on a distorted
triangular lattice is studied using a numerical-diagonalization method. The
network of interactions is the type; the interactions
are continuously controlled between the undistorted triangular lattice and the
dice lattice. We find new states between the nonmagnetic 120-degree-structured
state of the undistorted triangular case and the up-up-down state of the dice
case. The intermediate states show spontaneous magnetizations that are smaller
than one third of the saturated magntization corresponding to the up-up-down
state.Comment: 5pages, 5figures, to be published in J. Phys. Soc. Jp
Critical magnetization behaviors of the triangular and Kagome lattice quantum antiferromagnets
We investigate the quantum spin antiferromagnets on the triangular
and Kagome lattices in magnetic field, using the numerical exact
diagonalization. Particularly we focus on an anomalous magnetization behavior
of each system at 1/3 of the saturation magnetization. The critical exponent
analyses suggest that it is a conventional magnetization plateau on the
triangular lattice, while an unconventional phenomenon, called the
magnetization ramp, on the Kagome lattice.Comment: 4 figures, Phys. Rev. B Rapid Communications accepte
Third boundary of the Shastry-Sutherland Model by Numerical Diagonalization
The Shastry-Sutherland model --- the Heisenberg antiferromagnet on
the square lattice accompanied by orthogonal dimerized interactions --- is
studied by the numerical-diagonalization method. Large-scale calculations
provide results for larger clusters that have not been reported yet. The
present study successfully captures the phase boundary between the dimer and
plaquette-singlet phases and clarifies that the spin gap increases once when
the interaction forming the square lattice is increased from the boundary. Our
calculations strongly suggest that in addition to the edge of the dimer phase
given by and the edge of the Nel-ordered
phase given by , there exists a third boundary ratio
that divides the intermediate region into two parts,
where and denote dimer and square-lattice interactions,
respectively.Comment: 5 pages, 8 figures, to be published in J. Phys. Soc. Jp
Gapless Spin Excitations in the Kagome- and Triangular-Lattice Heisenberg Antiferromagnets
The kagome- and triangular-lattice Heisenberg antiferromagnets are
investigated using the numerical exact diagonalization and the finite-size
scaling analysis. The behaviour of the field derivative at zero magnetization
is examined for both systems. The present result indicates that the spin
excitation is gapless for each system.Comment: 12pages, 4figures, to be pblished in Physica
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