Critical dynamics of singlet excitations in a frustrated spin system
Abstract
We construct and analyze a 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. 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. The novel quantum critical behavior associated with singlet criticality discussed in this work can be relevant to a wide class of disordered quantum spin systems, such as antiferromagnets on Kagome, pyrochlore, and CAVO lattices.Keywords
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