Raghu, C and Rudra, Indranil and Ramasesha, S and Sen, Diptiman
(2000)
*Evaluation of low-energy effective Hamiltonian techniques for coupled spin triangles.*
In: Physical Review B, 62
(14).
pp. 9484-9492.

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## Abstract

Motivated by recent work on Heisenberg antiferromagnetic spin systems on various lattices made up of triangles, we examine the low-energy properties of a chain of antiferromagnetically coupled triangles of half-odd-integer spins. We derive the low-energy effective Hamiltonian to second order in the ratio of the coupling $J_2$ between triangles to the coupling $J_1$ within each triangle. The effective Hamiltonian contains four states for each triangle which are given by the products of spin-1/2 states with the states of a pseudospin 1/2. We compare the results obtained by exact diagonalization of the effective Hamiltonian with those obtained for the full Hamiltonian using exact diagonalization and the density-matrix renormalization group method. It is found that the effective Hamiltonian gives an accurate value for the ground-state energy only if the ratio $J_2/J_1$ is less than about 0.2 and that too for the spin-1/2 case with linear topology. The chain of spin-1/2 triangles shows interesting properties like spontaneous dimerization and several singlet and triplet low-energy ~possibly gapless! states which lie close to the ground state. We have also studied the spin-3/2 case and find the low-energy effective Hamiltonians (LEH’s) to be less accurate there than in the spin-1/2 case. Finally, we have studied nonlinear topologies where the LEH results deviate further from the exact results.

Item Type: | Journal Article |
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Additional Information: | Copyright of this article belongs to American Institute of Physics. |

Department/Centre: | Division of Chemical Sciences > Solid State & Structural Chemistry Unit Division of Physical & Mathematical Sciences > Centre for Theoretical Studies |

Date Deposited: | 01 Sep 2006 |

Last Modified: | 19 Sep 2010 04:30 |

URI: | http://eprints.iisc.ernet.in/id/eprint/8131 |

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