REVISITING THE SUPERCONDUCTING PHASE-DIAGRAM OF (TMTSF)(2)CLO4

We present results of a search for evidence of reentrance at high magn etic field of the superconducting state in the quasi-one dimensional o rganic superconductor (TMTSF)(2)ClO4, for a specific orientation of th e field at low temperature. This search was motivated by the theoretic al work of Lebed' and of Dupuis & Montambaux, and in part by that of T esanovic and coworkers, who predict novel magnetic field-temperature p hase diagrams in quasi-1-D and quasi-2-D superconductors in a strong m agnetic field. In the quasi-1-D case, a field directed both normal to the chains and along the layers is proposed to induce exotic oscillati ons of the critical temperature at high field, while for the 2-D case, quantum effects associated with Landau quantization lead to similar p redictions. We have investigated the superconducting transition in a q uasi-1-D candidate material, (TMTSF)(2)ClO4, to 0.06 K with field orie nted along the b'-axis (+/-0.02 degrees). From mostly constant field t emperature sweeps, we find positive curvature in H-c2(T) below about T -c/2. In addition, a resistivity decrease is observed to persist to 7 T, the highest field employed, with a slightly positive slope partial derivative H/partial derivative T above 5T. The possibility of these f eatures being representative of high field superconductivity is discus sed.