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The noncentrosymmetric ClO4 anions of the organic superconductor (TMTSF)2ClO4 order below 24K. The size of domains where the anions are ordered is substantially dependent on the cooling rate which is a key parameter for the stability of the low temperature electronic ground states. We study the effect of the cooling rate on the SC phase within a self consistent approach in the framework of the time dependent Ginzburg-Landau theory taking into account the superconducting fluctuations. We derive the superconducting transition temperature which is found to decrease with increasing cooling rate in agreement with recent experimental data.

We propose a theoretical model of quasi-one-dimensional superconductors, with attractive electron-electron interactions dominant in the singlet d-wave channel and sub-dominant in the pwave channel. We discuss, in the mean field approximation, the effect of a magnetic field applied perpendicularly to the direction of the lowest conductivity. The lowest free energy phase corresponds to a singlet d-wave symmetry in low fields, but to a triplet symmetry in high fields. A first order singlet-triplet phase transition is expected at moderate applied fields of a few teslas. We propose to ascribe the recent critical field and NMR experimental data, observed in superconducting (T M T SF )2ClO4 to such an effect.PACS numbers: 74.70. Tx, 74.25.Op, 74.20.Rp The nature of superconductivity in the family of the quasi-1D organic superconductors [1, 2, 3] (T M T SF ) 2 X (X = P F 6 , ClO 4 ,...) has been a long standing issue for the last three decades. There is still a debate whether it is a conventional superconductivity, with a completely gapped Fermi surface, or an unconventional one with points or lines of nodes on the gap. Many experiments have tried to address this question using different techniques such as NMR relaxation rate, thermal conductivity, non magnetic impurity effect on T c , Knight Shift and upper critical field measurements.The temperature dependence of the proton spin lattice relaxation rate, measured by Takigawa et al. [6] studied the effect of non magnetic impurities on the superconducting critical temperature T c [7], and showed unequivocally that the order parameter changes sign on the Fermi surface and that consequently the gap has nodes where it is zero on the Fermi surface. This is in complete agreement with a model of unconventional superconductivity in these organic materials.However, whether the pairing of the electrons in the superconducting state is in the singlet or the triplet symmetry remains an unsolved question. Measurements of the upper critical field of superconductivity in these materials [8,9,10] showed a superconducting state surviving up to a field as high as 9 T in the case of the P F 6 compounds [8], and at least 5 T in the case of the ClO 4 compounds [9]. These fields exceed by far the Clogston-Pauli paramagnetic limit [11] for homogeneous singlet superconductivity, which is estimated to be of the order of 1.84 T c , with a T c around 1.1 K in these materials. This result is a strong indication that at high magnetic fields superconductivity could not be of a homogeneous singlet type. Many theories [12,13,14] have been proposed to explain this behaviour by a triplet superconducting state, which is a non Pauli limited state. At low magnetic fields, however, besides the observation by Andres et al.[15] of a diamagnetic signal when the field is perpendicular to the chains indicating a singlet state, measurements of the Knight-Shift [16] showed a significant variation from the normal state behaviour of the spin susceptibility of Cooper pairs which decreased with decreasing temperatur...

We present transport measurements along the least conducting (c) direction of the organic superconductor (TMTSF)2ClO4 performed under an accurately aligned magnetic field in the low temperature regime. The experimental results reveal a two-dimensional confinement of the carriers in the (a,b) planes which is governed by the magnetic field component along the b ′ direction. This 2-D confinement is accompanied by a metal-insulator transition for the c axis resistivity. These data are supported by a quantum mechanical calculation of the transverse transport taking into account in self consistent treatment the effect of the field on the interplane Green function and on the intraplane scattering time.