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Le Journal de Physique Colloques

QUANTUM SPIN CHAINS WITH COMPOSITE SPIN

Jenő Sólyom, JUSSI TIMONEN

Published Dec 1, 1988• 0 citations
Publisher

Abstract

The ground state of quantum spin chains with two spin-1/2 operators per site is determined from finite chain calculations and compared to predictions from the continuum limit. As particular cases, results for the spin-1 Heisenberg chain, the spin-1 model with bilinear and biquadratic exchange and the extended Hubbard model are analysed.
DOI
10.1051/jphyscol:19888631

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Additional three-site exchange interactions, naturally arising, e.g., in the strong-coupling expansion of the two-band Hubbard model and in various effective spin Hamiltonians, may stabilize various exotic spin phases which are not typical for the pure Heisenberg models on frustrated lattices and/or with extra biquadratic exchange terms. The reason is hidden in some specific features of the isotropic three-site exchange interactions, such as the promotion of collinear spin configurations as well as the reinforcing tendency towards clustering of the quantum spins on the shortest exchange bonds. As a result, systems with integer and half­integer composite spins in the unit cell might be expected to support different quantum phase diagrams. In this work, we study this phenomenon by comparing the quantum phase diagrams of two Heisenberg chains with extra three-site exchange terms and two different alternating pairs of site spins S and σ [( S , σ) = and ( ], resulting in half-integer and integer cell spins S + σ , respectively.