QUROPE Quantum Information Processing and Communication in Europe

We construct a family of simple fermionic projected entangled pair states (fPEPS) on the square lattice with bond dimension D=3 which are exactly hole-doped resonating valence bond (RVB) wavefunctions with short-range singlet bonds. Under doping the insulating RVB spin liquid evolves immediately into a superconductor with mixed d+is pairing symmetry whose pair amplitude grows as the square-root of the doping. The relative weight between s-wave and d-wave components can be controlled by a single variational parameter c. We optimize our ansatz w.r.t. c for the frustrated t−J1−J2 model (including both nearest and next-nearest neighbor antiferromagnetic interactions J1 and J2, respectively) for J2≃J1/2 and obtain an energy very close to the infinite-PEPS state (using full update optimization and same bond dimension). The orbital symmetry of the optimized RVB superconductor has predominant d-wave character, although we argue a residual (complex s-wave) time reversal symmetry breaking component should always be present. Connections of the results to the physics of superconducting cuprates and pnictides are outlined.