The superconducting state in (TMTSF)2PF6 in high magnetic field

The resistive upper critical field along the b-axis (H c2 //b) in (TMTSF) 2 PF 6 is investigated in detail in fields to 17.5 T and temperatures to T/T c ∼ 1/60, at various pressures near the border between spin density wave and metallic states. Previously, we had obtained a novel crossover where H c2 //b exceeded both H c2 //a, in contrast to band structure, and the Pauli paramagnetic limit μ o H p 2 T. Remarkably, in an optimum pressure setting reported here, it is found that the onset of superconductivity persists up to 9 T (> 4 H p ), which strongly suggests triplet Cooper pairing. Strong upward curvature with nearly diverging behaviour of the critical field also seem to suggest a field-dependent dimensional crossover, although the H c2 enhancement is considerably more than that predicted by recent theories.