Superconducting diamagnetism is samples of (SN)/sub x/, TaSe3 and NbSe3

The highly anisotropic metals (SN)/sub x/, TaSe3 and NbSe3 have shown low temperature behavior which could be associated with unusual superconducting properties. The present susceptibility measurements, made using a very sensitive SQUID magnetometer, were undertaken to add to the understanding of these new materials and to investigate the nature of superconductivity in the unusual systems which these materials present. While previous work has indicated a distinctly one-dimensional character of the superconductivity of (SN)/sub x/, the present magnetic studies show - by the observation of a Meissner effect - that the superconductivity below 200 mK is three - dimensional. The results suggest a coupling transition in which individual fibers, superconducting below about 300 mK, become superconductively coupled at a lower temperature give phase coherence throughout a bulk sample. The result is supported by the unusual field and temperature dependences of the ac and dc susceptibilities and by the observation of a penetration depth which is comparable to the diameter of the crystals. A similiar coupling transition is observed in brominated (SN)/sub x/, in which the fibers are found to be somewhat more strongly coupled. While such a transition has been predicted theoretically, this is the first observation of a fiber to bulk coupling transition. The present work is consistent with the observations of others, and explains some of the more puzzling features of previous work. The primary result of the investigation of samples of TaSe3 and NbSe3 is the observation of superconducting diamagnetism and flux trapping indicating long range, stable superconducting phase coherence in the samples