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Critical Dynamics of Singlet Excitations in a Frustrated Spin System

Valeri N. Kotov·Michael E. Zhitomirsky·Oleg P. Sushkov
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Abstract

We construct and analyze a two-dimensional frustrated quantum spin model with plaquette order, in which the low-energy dynamics is controlled by spin singlets. At a critical value of frustration the singlet spectrum becomes gapless, indicating a quantum transition to a phase with dimer order. This T=0 transition belongs to the 3D Ising universality class, while at finite temperature a 2D Ising critical line separates the plaquette and dimerized phases. The magnetic susceptibility has an activated form throughout the phase diagram, whereas the specific heat exhibits a rich structure and a power law dependence on temperature at the quantum critical point. We argue that the novel quantum critical behavior associated with singlet criticality discussed in this work can be relevant to a wide class of quantum spin systems, such as antiferromagnets on Kagome and pyrochlore lattices, where the low-energy excitations are known to be spin singlets, as well as to the CAVO lattice and several recently discovered strongly frustrated square-lattice antiferromagnets.

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Valeri N. Kotov, Michael E. Zhitomirsky, Oleg P. Sushkov. 2000-11-03. Critical Dynamics of Singlet Excitations in a Frustrated Spin System. https://doi.org/10.1103/physrevb.63.064412

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