Exotic superconductivity in strongly anisotropic correlatedorganic metals in the vicinity of insulating phases

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Unconventional superconductivity with the order parameter oscillating in momentum or real space, which is expected to be realized in conducting materials with strong electronic correlations, has lately been a subject of great interest. Organic metals possess a number of features, which make them particularly attractive model systems for systematically studying the subtle interplay between superconductivity and other instabilities of the normal metallic state.The main goal of this project is to reveal manifestations of exotic superconductivity and its interplay with other ordering instabilities in these materials. The compounds chosen for studies exhibit superconductivity in the immediate vicinity to and even coexisting with other ordered ground states: the charge-density-wave metal alpha-(ET)2KHg(SCN)4; the antiferromagnetic metal kappa-(BETS)2FeCl4; the magnetically ordered (probably Mott) insulator kappa-(BETS)2Mn[N(CN)2]3. The project aims at clarifying the influence of the competing orderings on superconducting (SC) properties of these compounds. The relative strength of the ordering instabilities in all these compounds is sensitive to pressure. This provides a convenient opportunity for studying the dependence of SC properties on the pressure-controlled proximity to the density-wave or magnetic ordering.Due to the very high electronic anisotropy, the orbital pair-breaking effect of a magnetic field parallel to layers is strongly suppressed in these materials. In this situation the Pauli paramagnetic effect on charge carriers is expected to be the dominant pair-breaking mechanism. If the samples are clean enough, this will provide the necessary and sufficient condition for a field-induced transition from a homogeneous SC state into the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with an order parameter oscillating in real space. The search for the FFLO state in the above mentioned compounds is another major objective of this project.Two of the chosen compounds are characterized by very low SC critical temperatures (about 0.1K). This facilitates straightforward measurements of the critical fields since the vortex dynamics effects in transport and magnetization, which usually cause big problems in quasi-two-dimensional superconductors, are strongly suppressed in the whole SC range. The research project is planned in cooperation with partners at Chernogolovka, Russia, who will deliver the crystals for the physical investigations and develop novel materials which will also be tested within the project. The experiments on kappa-(BETS)2Mn[N(CN)2]3 will also be conducted in cooperation with the Russian partners.