arXiv:0807.3189 · Physical Review B
Order and disorder in AKLT antiferromagnets in three dimensions
S. A. Parameswaran, Shivaji L. Sondhi, Daniel P. Arovas
Abstract
The models constructed by Affleck, Kennedy, Lieb, and Tasaki (AKLT) [Phys. Rev. Lett. 59, 799 (1987)] describe a family of quantum antiferromagnets on arbitrary lattices, where the local spin $S$ is an integer multiple $M$ of half the lattice coordination number. The equal-time quantum correlations in their ground states may be computed as finite temperature correlations of a classical $O(3)$ model on the same lattice, where the temperature is given by $T=1/M$. In dimensions $d=1$ and 2 this mapping implies that all AKLT states are quantum disordered. We consider AKLT states in $d=3$ where the nature of the AKLT states is now a question of detail depending upon the choice of lattice and spin; for sufficiently large $S$ some form of N\'eel order is almost inevitable. On the unfrustrated cubic lattice, we find that all AKLT states are ordered, while for the unfrustrated diamond lattice the minimal $S=2$ state is disordered while all other states are ordered. On the frustrated pyrochlore lattice, we find (conservatively) that several states starting with the minimal $S=3$ state are disordered. The disordered AKLT models we report here are a significant addition to the catalog of magnetic Hamiltonians in $d=3$ with ground states known to lack order on account of strong quantum fluctuations.