Revival of superconductivity in high magnetic fields and a possible p-wave pairing in (TMTSF)₂PF₆

From the BCS theory, we derive an equation which accounts for quantum effects of an electron motion along open Fermi surfaces and determines the upper critical field H_c2^⊥(T) perpendicular to the chains of a quasi-one-dimensional conductor. This equation demonstrates two unusual phenomena: (1) restoration of superconductivity at H>H_c2^⊥(0) in p-wave superconductors, where H_c2^⊥(0) is the quasiclassical upper critical field; (2) surviving of superconductivity at H_c2^⊥(0), H_p<H<H_p^LOFF in s-wave superconductors, where H_p is the Clogston-Chandrasekhar paramagnetic limiting field; the critical field H_p^LOFF is introduced in the paper. An analysis of recent experimental data by I. J. Lee, M. J. Naughton, G. M. Danner, and P. M. Chaikin [Phys. Rev. Lett. 78, 3555 (1997)] shows that superconductivity significantly exceeds H_p^LOFF for b direction of a magnetic field in (TMTSF)₂PF₆. This demonstrates a strong suppression of the Pauli pair breaking effects and may reflect a p-wave pairing of electrons.