We study possible paramagnetic phases of antiferromagnets on the Shastry-Sutherland lattice by a gauge-theoretic analysis of fluctuations in a theory with $\mathrm{Sp}\mathrm{}\left(2N\right)\mathrm{}$ symmetry. In addition to the familiar dimer phase, we find a confining phase with plaquette order and a topologically ordered phase with deconfined $S=1/2\mathrm{}$ spinons and helical spin correlations. The deconfined phase is contiguous to the dimer phase and in a regime of couplings close to those found in the insulator ${\mathrm{SrCu}}_2({\mathrm{BO}}_3{)}_2.$ We suggest that a superconductor obtained by doping this insulator with mobile charge carriers will be an attractive candidate for observing the anomalous magnetic flux properties associated with topological order.

• Received 11 March 2001

DOI:https://doi.org/10.1103/PhysRevB.64.134407