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Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

A. Brühl·B. Wolf·V. Pashchenko·M. Anton·C. Gross·W. Assmus·R. Valenti·S. Glocke·A. Klümper·T. Saha-Dasgupta·B. Rahaman·M. Lang
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Abstract

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)$_2$P$_2$O$_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $Δ$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $Δ$, $\partial S^{m}/ \partial Δ$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $Δ$.

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A. Brühl, B. Wolf, V. Pashchenko, M. Anton, C. Gross, W. Assmus, R. Valenti, S. Glocke, A. Klümper, T. Saha-Dasgupta, B. Rahaman, M. Lang. 2008-01-18. Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains. https://doi.org/10.1103/physrevlett.99.057204

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