Motivated by the ongoing investigation of SrCu${}_2$(BO${}_3$)${}_2$ under pressure, we study a variant of the two-dimensional Shastry-Sutherland (SS) spin-$1/2$ model with two types of dimers. Combined with the frustration of the SS model, this modification induces, in a large parameter range, a dimensional reduction at low energies, with nearly decoupled effective $S=1$ Haldane chains forming along one of the diagonals of the lattice. We also present evidence that the intermediate plaquette solid phase of the undistorted SS model remains stable in a finite region of the phase diagram.

• Received 23 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.140414