Martin, C., Cho, K., Mihut, I. et al. J Low Temp Phys (2006) 142: 257. doi:10.1007/BF02679504
Using a Tunnel Diode Oscillator technique, we have measured the effect of a parallel magnetic field on the in-plane rf penetration depths in organic [α-(BEDT-TTF)2NH4Hg(SCN)4 and k-(BEDT-TTF)2Cu(NCS)2] and heavy fermion (CeCoIn5) superconductors. We show that in this particular geometry, the effects due to vortex activity are minimized. The penetration depth is then governed by the density of superconducting carriers. It is shown in many experiments including rf penetration depth measurement that α-(BEDT-TTF)2NH4Hg(SCN)4 and CeCoIn5 have s-wave and d-wave pairing symmetries, respectively. The pairing symmetry of k-(BEDT-TTF)2-Cu(NCS)2, however, is still an unsolved matter, showing inconsistent results. In this paper, the penetration depth of k-(BEDT-TTF)2Cu(NCS)2 is shown to be more similar to α-(BEDT-TTF)2NH4Hg(SCN)4 than to CeCoIn5, suggesting the pairing is nodeless.