Upper Critical Field and Shubnikov-de Haas (SdH) Quantum Oscillation Studies in a New quasi 2D Organic Superconductor*

The upper critical field and SdH quantum oscillations have been studied in the new layered organic superconductor β″-(BEDT-TTF)₂[(H₂O)Cr(C₂O₄)₃]18-crown-6 by measuring the in-plane rf-penetration depth with the tunnel diode oscillator technique. The reported upper critical field is 8T, above the calculated Clogston-Chandrasekhar limit (Hp). This, along with the strong 2D nature of this crystal & its wide anion layers suggest that there could be a possibility of an inhomogeneous FFLO superconducting state in this material. We will highlight data when the applied magnetic field is parallel to the conducting layers at low temperature using a 32T superconducting magnet at the National High Magnetic Field Laboratory. We will also present SdH quantum oscillation data when the applied field is perpendicular to the conducting layers and to compare the Fermi surface with the related compounds, λ-(BETS)₂GaCl₄ and К-(ET)₂Cu[N(CN)₂]Br, other layered organics. The difference in Fermi surface topology will be discussed in relation to the existence of the FFLO state.