mu SR studies of intercalated HfNCl superconductor

Muon spin relaxation measurements of the magnetic field penetration depth l ambda have been performed in a quasi two-dimensional (2-d) superconductor b ased on HfNCl intercalated with Li and organic molecules. The relaxation ra te sigma(T --> 0) similar to 0.5 mu s(-1) was obtained with transverse fiel ds applied perpendicular to the aligned HfN planes. Using the relation sigm a proportional to lambda(-2) proportional to n(s2d)/m* (2-d superconducting carrier density/effective mass), we deduced the 2-d Fermi temperature T-F2 d. The ratio Tc/T-F2d for the HfNCl-(Li) system is very close to those in t wo other quasi-2-d superconductors, YBa2Cu3O7 and (BEDT-TTF)(2)-X. Compared to the Kosterlitz-Thouless (KT) transition temperature T-KT = T-F2d/8 for the limit of strong coupling, T-c's of these systems are reduced by a facto r of 3-4, indicating the importance of carrier overlapping and/or 3-d coupl ing. (C) 2000 Elsevier Science B.V. All rights reserved.