Some Properties of the (TMTSF)₂X Superconductors

Abstract

Abstract Measurements of the anisotropy of the critical field in (TMTSF)2X superconductors are presented. The results show that the a axis Hc2 is Pauli limited based on a Tc near 1K. The large energy gap obtained from tunneling data is therefore thermodynamically untenable in terms of the present critical field studies and the superconductivity is singlet rather than triplet. Moreover, we find that low levels of irradiation induced defects eliminate the superconductivity in the ClO4 and PF6 salts and leave the thermopower of the ClO4 salt below 100K unchanged. These results are incompatible with the proposal for 1D superconducting fluctuations below 40K. A discussion of the arguments for and against the occurance of superconducting fluctuations in the (TMTSF)2X salts is given with emphasis on the role of interchain interactions and other possible interpretations of the tunneling data.