Magnetic field-temperature phase diagram of the quasi-two-dimensional organic superconductor λ-(BETS)2GaCl4 studied via thermal conductivity -: art. no. 134503

The thermal conductivity kappa of the quasi-two-dimensional (Q2D) organic superconductor lambda-(BETS)(2)GaCl4 [BETS = bis(ethylenedithio)tetraselenfulvalene] was studied in the magnetic field H applied parallel to the Q2D plane. The phase diagram determined from this bulk measurement shows notable dependence on the sample quality. In dirty samples the upper critical field H-c2 is consistent with the Pauli paramagnetic limiting, and a sharp change is observed in kappa(H) at H-c2parallel to. In contrast, in clean samples H-c2(T) shows no saturation towards low temperatures and the feature in kappa(H) is replaced by two slope changes reminiscent of second-order transitions. The peculiarity was observed below similar to0.33T(c) and disappeared on field inclination to the plane when the orbital suppression of superconductivity became dominant. This behavior is consistent with the formation of a superconducting state with spatially modulated order parameter in clean samples.