Thermodynamic properties of quasi-two-dimensional organic superconductors

High-resolution specific-heat data of the organic superconductor kappa-(ET)(2)Cu(NCS)(2) (T-c = 9.3 K) can reasonably well be described by strong-coupling BCS theory. In line with our previous results for three other organic superconductors the electronic contribution of the specific heat vanishes exponentially towards low temperatures providing evidence for a fully-gapped order parameter. The thermal conductivity kappa of kappa-(ET)(2)Cu[N(CN)(2)]Br increases strongly in the superconducting state below T-c = 11.5 K indicating the substantial scattering of phonons by quasiparticles in the normal state. Down to the lowest temperatures (T approximate to 0.25 K) no T-3 dependence of kappa is observed. (C) 2002 Elsevier Science B.V. All rights reserved.