t-J model on the Shastry-Sutherland lattice

The spin-1/2 Heisenberg model on the Shastry Sutherland (SS) lattice is a frustrated system that has a spin gap state. Our previous study has shown that the $t$-$J$ model on the SS lattice does not exhibit hole-pairing when the diagonal hopping term t' is positive.[Phys.Rev.B{\bf 69}, 180403 (2004)]. It demonstrates that the existence of a spin gap does not necessarily lead to hole pairing. In this project, we investigate the case where t' is negative. The method we use is numerical diagonalization on a 32-site SS lattice with periodic boundary conditions. Our result shows that in the present case the distortion on the spin background due to a mobile hole is different from the previous case where t' is positive. The frustration due to hopping motion of the hole does not favor dimerized spin order which exists at half-filling. As a result, other spin orders competing with the dimerized spin order may be enhanced. We will also study the possibility of hole-pairing in the present case.