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The upper critical fields in the direction parallel to superconducting plane, Hc2″, of the layered salts κ-(BEDT-TTF)2X (X=Cu(NCS)2, Cu[N(CN)2]Br) and κ-(BEDT-TTF)4-Hg2.89Br8 far exceed the BCS Pauli paramagnetic limit and show variety of temperature (T) dependence at ambient pressure. We extended the studies of the Hc2″(T) diagrams for all main κ-(BEDT-TTF)2X superconductors by applying pressure. Emphasis is placed on the behaviour at low T and in high magnetic fields. The origin of the exceeding the BCS Pauli paramagnetic limit is discussed. The dependence of Hc2″ on the field direction within the plane is also presented.

The superconductivity of the layered organic salt β-(BOA-TTP) 2 SbF 6 , where BDA-TTP is a new donor molecule centred with tetrathiapentalene (TTP) skeleton, has been studied through the measurements of the interlayer resistivity, magnetic susceptibility and thermal conductivity in oriented magnetic fields. The non-BCS behaviour of the specific heat suggests unconventional nature of the superconductivity in the compound. The variance of the temperature dependence of H c2 determined from measurement of various physical parameters is found. The angle-dependent magnetoresistance oscillation observed in the normal state exhibits complexity representing the low symmetry of the electronic structure.

The superconductivity of quasi one-dimensional salt (DMET-TSeF) 2 AuI 2 was studied in the oriented magnetic fields through the resistive measurement. The upper critical fields H c2 in the magnetic fields parallel to the highest and intermediate conductive a - and c -axes tend to exceed the Pauli paramagnetic limit. However, it is difficult to determine these values because the behaviour below 0.3 K is obscured by an electronic phase transition. The coherence lengths are evaluated from the slopes of H c2 ( T ) curves near T c as ξ a (0)≈100 nm, ξ b (0)≈2 nm, ξ c (0)≈30 nm.

The resistive transition in two-dimensional superconductor α-(BEDT-TTF) 2 NH 4 Hg(SCN) 4 was studied under magnetic fields applied precisely parallel to the plane. This enables to suppress the effect of the orbital pair breaking and that of the vortex dynamics for the in-plane resistance measurement. At low temperatures ( 1.8 T). a hidden superconducting state where the resistivity is insensitive to temperature remains up to 5.5 T.

The upper critical field of κ-(ET) 4 Hg 2.89 Br 8 was studied under a parallel magnetic field up to 24 T in the temperature region down to 0.5 K. The data obtained at 0.5 K indicate that the value tends to saturate toward 0 K but exceeds the Pauli paramagnetic limit based upon BCS weak coupling model, giving a value more than two times.

The resistive transition of α -(ET) 2 NH 4 Hg(SCN) 4 under a magnetic field applied exactly parallel to the superconducting sheet was studied. The out-of-plane resistivity was found not to exhibit a resistivity decrease associated with the superconductivity within the sheet due to the vortex-flow dissipation.