Unconventional superconducting states on doped Shastry-Sutherland lattice

By using a renormalized mean-field theory, we investigate the phase diagram of $t$-$t'$-$J$-$J'$ model on two dimensional Shastry-Sutherland lattice which are topologically equivalent to synthesized material $\mathrm{SrCu_2(BO_3)_2}$. We find that the symmetry of superconductivity ground state depends on the frustration amplitude $\eta=t'/t$ and doping concentration. For weak to intermediate frustration, $d_{x^2-y^2}$-wave pairing symmetry is robust in a large parameter region. Around the symmetric point $|\eta|=1$, d-wave, $s$-s-wave pairing as well as staggered flux may serve as ground state by varying the doping level. There is a first-order transition between these distinct ground states. For larger frustration $|\eta|>1$, the ground state has an $s$-s-wave symmetry for both hole and electron doping.