Quantum topological excitations: from the sawtooth lattice to the Heisenberg chain |
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Authors: | SA Blundell MD Núñez-Regueiro |
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Institution: | (1) Département de Recherche Fondamentale sur la Matière Condensée, CEA-Grenoble/DSM 17 rue des Martyrs, 38054 Grenoble Cedex 9, France, FR;(2) Laboratoire de Physique des Solides, batiment 510, Université Paris-Sud, 91405 Orsay Cedex, France, FR |
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Abstract: | From the recently determined structure of the delafossite YCuO2.5, we argue that the Cu-O network has nearly independent Δ chains but with different interactions between the s = 1/2 spins. Motivated by this observation, we study the Δ chain for different ratios of the base-base and base-vertex interactions,
J
bb/J
bv. By exact diagonalization and extrapolation, we show that the elementary excitation spectrum is the same for total spins
S
tot = 0 and 1, but not for S
tot = 2, and has a gap only in the interval 0.4874(1) ⩽ J
bb/J
bv ⩽ 1.53(1). The gap, known to be dispersionless for J
bb = J
bv, is found to acquire increasing k-dependence as J
bb/J
bv moves away from unity.
Received 29 October 2002 / Received in final form 14 January 2003 Published online 6 March 2003
RID="a"
ID="a"e-mail: sblundell@cea.fr
RID="b"
ID="b"e-mail: nunezreg@lps.u-psud.fr |
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Keywords: | PACS 75 50 Ee Antiferromagnetics – 75 10 Jm Quantized spin models – 75 10 -b General theory and models of magnetic ordering – 75 40 Mg Numerical simulation studies |
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