Importance of Interlayer Effects for Tc in kappa-(ET)2 X Superconductors

摘要

We report high-resolution measurements of the linear thermal-expansioncoefficient perpendicular to the conducting planes, (alpha)(perpendicular)(T), on single crystals of the superconductors (kappa)-(ET)(sub 2)X with X=I(sub 3), CU(NCS)(sub 2) and Cu(N(CN)(sub 2))Br. For all three compounds we find pronounced negative phase-transition anomalies at (Tc). Using the Ehrenfest relation, the uniaxial-pressure coefficients of (Tc) can be determined. We find that interlayer effects are of crucial importance for (Tc) in this class of materials. Regarding also interlayer effects we compare our results with recent theories addressing the p-T phase diagram.