THERMAL-EXPANSION IN SINGLE-CRYSTALS OF KAPPA-(BEDT-TTF)(2)CU(NCS)(2)IN MAGNETIC-FIELDS UP TO 6 TESLA

The linear thermal expansion coefficients alpha(i) (i=a,b,c) of singl e crystals of the organic superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) (T-c=9.15K) have been measured in the temperature range from 2 to 300 K, by means of capacitive dilatometry. At T-c, we resolved second orde r jumps Delta alpha(i), which disappear in magnetic fields above H-c2. From the initial slopes dH(c2)/dT parallel and perpendicular to the s uperconducting layers the Ginzburg-Landau coherence lengths xi(paralle l to)(0) = 67 Angstrom and xi(perpendicular to) (0) = 7.3 Angstrom wer e detennined. Via Ehrenfest's relation it is possible to deduce the un iaxial stress dependence of T-c, which was found to be negative in the a-direction (partial derivative T-c/partial derivative sigma(a*) = - 3.20K/kbar), positive in the c-direction (partial derivative T-c/parti al derivative sigma(c) = 1.46 K/kbar) and zero in the b-direction.