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Gapless points of dimerized quantum spin chains: Analytical and numerical studies

Chandra, Ravi V and Sen, Diptiman and Surendran, Naveen (2006) Gapless points of dimerized quantum spin chains: Analytical and numerical studies. In: Physical Review B, 74 (18). 184424:1-9.

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We study the locations of the gapless points which occur for quantum spin chains of finite length (with a twisted boundary condition) at particular values of the nearest-neighbor dimerization, as a function of the spin S and the number of sites. For strong dimerization and large values of S, a tunneling calculation reproduces the same results as those obtained from more involved field theoretic methods using the nonlinear \sigma -model approach. A different analytical calculation of the matrix element between the two Néel states gives a set of gapless points; for strong dimerization, these differ significantly from the tunneling values. Finally, the exact diagonalization method for a finite number of sites yields a set of gapless points which are in good agreement with the Néel state calculations for all values of the dimerization, but the agreement with the tunneling values is not very good even for large S. This raises questions about possible corrections to the tunneling results.

Item Type: Journal Article
Publication: Physical Review B
Publisher: The American Physical Society
Additional Information: Copyright of this article belongs to The American Physical Society.
Department/Centre: Division of Physical & Mathematical Sciences > Centre for High Energy Physics
Date Deposited: 21 May 2008
Last Modified: 19 Sep 2010 04:45
URI: http://eprints.iisc.ac.in/id/eprint/14018

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