Anisotropic superconductivity in /spl kappa/-(BET-TTF)/sub 2/Cu(NCS)sub 2/

Summary form only given. In these several years, the question whether the mechanism of the superconductivity in organic salts is of the conventional BCS type or not has been attracting wide interest. Several experiments aiming at the clarification of the type of superconductivity were made, but the results were controversial with one another. In our previous work, we made precise measurements of complex susceptibility with low-frequency ac-field less than lower critical field for single crystals of /spl kappa/-(BET-TTF)/sub 2/X (X=Cu(NCS)sub 2/, Cu[N(CN)/sub 2/Br), and found that the penetration depth followed a power law at low temperatures. This result gives the evidence for anisotropic superconductivity with points or lines of nodes of the gap parameter on the Fermi surface. In contrast, other results indicating BCS behaviours were also reported. While we believe that the present method is most reliable to get the intrinsic penetration depth, there remain still some ambiguities related to the possible effect of geomagnetism on susceptibility measurements and the sample dependence of the absolute values of the penetration depth. To clarify these problems, we set the magnetic shield made of /spl mu/-metal and measured susceptibility of the title compound from differnt batches. As a consequence, we have confirmed that the temperature dependence of the penetration depth in the absence of geomagnetism follows a power law which agrees with the behavior expected for an anisotropic superconductor.