Triplet electron pairing and anisotropic spin susceptibility in organic superconductors (TMTSF)2X

Abstract

We argue that the (TMTSF)2PF6 compound under pressure is likely a triplet superconductor with a vector order parameter d(k)≡(da(k)≠0, dc(k)=?, db′(k)=0); |da(k)|>|dc(k)|. It corresponds to an anisotropic spin susceptibility at T=0: χb′=χ0, χa≪χ0, where χ0 is its value in a metallic phase. (The spin-quantization axis, z, is parallel to a so-called b′ axis.) We show that the suggested order parameter explains why the upper critical field along the b′ axis exceeds all paramagnetic limiting fields, including that for a nonuniform superconducting state, whereas the upper critical field along the a axis (a⊥b′) is limited by the Pauli paramagnetic effects [I. J. Lee, M. J. Naughton, G. M. Danner, and P. M. Chaikin, Phys. Rev. Lett. 78, 3555 (1997)]. The triplet order parameter is in agreement with the recent Knight shift measurements by I. J. Lee et al. as well as with the early results on a destruction of superconductivity by nonmagnetic impurities and on the absence of the Hebel-Slichter peak in the NMR relaxation rate.

Source-reported materials — not catalogue approval

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