Mixed order parameters, accidental nodes and broken time reversal symmetry in organic superconductors: a group theoretical analysis.

We present a group theoretical analysis of several classes of organic superconductor. We predict that highly frustrated organic superconductors, such as κ-(ET)(2)Cu(2)(CN)(3) (where ET is BEDT-TTF, bis(ethylene-dithio)tetrathiafulvalene) and β'-[Pd(dmit)(2)](2)X, undergo two superconducting phase transitions, the first from the normal state to a d-wave superconductor and the second to a d+id state. We show that the monoclinic distortion of κ-(ET)(2)Cu(NCS)(2) means that the symmetry of its superconducting order parameter is different from that of orthorhombic κ-(ET)(2)Cu[N(CN)(2)]Br. We propose that β'' and θ phase organic superconductors have d(xy)+s order parameters.