We point out that (TMTSF)2PF6 compound at P ≃ 6 kbar is possibly a triplet superconductor with the vector order parameter d = (dx ≠ 0, dy ,dz = 0). It corresponds to an anisotropic spin susceptibility in a superconducting state: χb′(z) = χ0, χa(x) ≠ χ0, where χ0 is its value in a metallic phase. (Here, the spin quantization axis, z, is parallel to the easy axis, b′, of an antiferromagnetic SDW phase existing at P = 0). It is shown that the suggested order parameter can explain why the upper critical field along b′-axis (I.J. Lee, M.J. Naughton, G. Danner, and P.M. Chaikin, Phys. Rev. Lett. 78, 3555 (1997)) exceeds all paramagnetic limiting fields (including that for a non-uniform superconductivity) whereas the upper critical field along the a-axis is restricted by the Pauli paramagnetic effects. The triplet order parameter is consistent with the earlier results on a destruction of superconductivity by nonmagnetic impurities and the absence of the Hebel-Slichter peak in the NMR data as well as with the recent Knight shift measurements by S. Brown et al and by I. J. Lee et al.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering