We introduce and analyze a variational wave function for quasi two-dimensional κ-(ET)2 organic salts containing strong local and nonlocal correlation effects. We find an unconventional superconducting ground state for intermediate charge carrier interaction, sandwiched between a conventional metal at weak coupling and a spin liquid at larger coupling. Most remarkably, the excitation spectrum is dramatically renormalized and is found to be the driving force for the formation of the unusual superconducting state.PACS numbers: 74.70. Kn,74.20.Mn,71.27.+a The proximity to a Mott insulating phase affects the behavior of a correlated material in a fundamental way [1,2]. Since most Mott insulators are also magnetically ordered, it is often not clear whether unconventional behavior observed in nearby phases is due to the proximity to a Mott transition, to a magnetic phase transition, or a combination of both. Ideal materials to sort this out are obviously spin liquids, systems where the Mott insulating phase is magnetically disordered. Recently, such behavior was found in the magnetically frustrated, insulating organic charge transfer salt κ-(ET) 2 Cu 2 (CN) 3 by Shimizu et al. [3]. No magnetic long-range order was found down to T ≈ 30 mK. While the low-T susceptibility is suppressed, consistent with the opening of a spin gap, the observed power-law dependence, 1/T 1 ∝ T 2 , of the NMR-spin liquid relaxation rate[3] supports gapless (possibly nodal) excitations of the spin liquid. Under pressure, κ-(ET) 2 Cu 2 (CN) 3 becomes, like many similar κ-(ET) 2 X systems [4,5,6], a superconductor [7].In quasi two-dimensional κ-(ET) 2 X salts [4,5,6] dimers of ET = bis[ethylenedithio]-tetrathiafulvalene molecules are arranged in an anisotropic triangular lattice, with a charge state of one hole per dimer. The insulating state is, in most cases, antiferromagnetically ordered and separated from a pressure induced superconducting phase by a first order transition [8]. In the superconducting state a number of experiments strongly support the existence of nodes of the pairing gap [9,10,11,12,13,14,15,16]. A gap with nodes was determined in spin fluctuation theories [17,18,19,20,21]; the location of the nodes of most of these calculations [17,18,19,20] was however in disagreement with experiments [14,15]. More importantly, the absence of magnetic long range order in κ-(ET) 2 Cu 2 (CN) 3 and the rather strong first order transition to an antiferromagnet in other systems, seem to be at odds with key assumptions of the spin fluctuation approach.In this paper we introduce and analyze a variational resonating valence bond (RVB) wave function for sys- , and superconducting order parameter, ψs, as a function of U/t. For U/t < ∼ 8.5 the system is a Fermi liquid metal. Pairing and superconductivity build up in the intermediate coupling regime for U/t ∼ 8 − 10 in a non-BCS fashion. While the pairing amplitude grows with U/t, superconductivity is non-monotonic. For U/t > ∼ 10, ψs is negligible and the system becomes a spin liquid.tems close to...