Indications of unconventional superconductivity in doped and undoped triangular antiferromagnets

The possibility of superconductivity in doped and undoped triangular antiferromagnets is discussed. Using the Bethe-Salpeter (BS) equation, it is shown that the exchange of random-phase approximation paramagnons on a triangular lattice Hubbard model leads to strong pairing correlations at and near half filling. The dominant states for this system correspond to d-wave singlet (even-frequency) and s-wave triplet (odd-frequency) pairing. Analytical techniques applied to the hole-doped t-J model yield similar results. A t₁-t₂ Hubbard model interpolating between square (t₁=0) and triangular (t₁=t₂) lattices has a tendency to only d-wave singlet pairing for t₁/t₂<~0.8. Experimental consequences for organic compounds κ-(BEDT-TTF)₂X are discussed.