From spin-Peierls to superconductivity: (TMTTF)(2)PF6 under high pressure

The nature of the attractive electron-electron interaction, leading to the formation of Cooper pairs in unconventional superconductors, has still to b e fully understood and is subject to intensive research. Here we show that the sequence spin-Peierls, antiferromagnetism, superconductivity observed i n (TMTTF)(2)PF6 under pressure makes the (TM)(2)X phase diagram universal. We argue that the suppression of the spin-Peierls transition under pressure , the close vicinity of antiferromagnetic and superconducting phases at hig h pressure, as well as the existence of critical antiferromagnetic fluctuat ions above T-c strongly support the intriguing possibility that the interch ain exchange of antiferromagnetic fluctuations provides the pairing mechani sm required for bound charge carriers.