5 research outputs found
Weak antiferromagnetism and dimer order in quantum systems of coupled tetrahedra
We analyze the phases of an S=1/2 spin model on a lattice of coupled
tetrahedra. The presence of both Heisenberg and antisymmetric,
Dzyaloshinsky-Moriya interactions can lead to two types of symmetry-broken
states: non-magnetic dimer order and, unexpectedly, exotic 4 sub-lattice weak
antiferromagnetic order - a state with a generically small ordered moment and
non-zero chirality. External magnetic field also induces weak
antiferromagnetism co-existing with strong dimer correlations in the ground
state.
These states are formed as a result of broken Ising symmetries and exhibit a
number of unusual properties.Comment: 5 pages, 4 figures; final version to appear in Phys. Rev.
Critical Dynamics of Singlet Excitations in a Frustrated Spin System
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.Comment: 5 pages, 5 figures, additional discussion and figure added, to appear
in Phys. Rev.