Bulk Kosterlitz-Thouless Type Molecular Superconductor β″-(BEDT-TTF)[(HO)(NH)Cr(CO)]·18-crown-6.

A new molecular superconductor, β″-(BEDT-TTF)[(HO)(NH)Cr(CO)]·18-crown-6, has been synthesized from the organic donor molecule BEDT-TTF with the anion Cr(CO). The crystal structure consists of conducting organic layers of BEDT-TTF molecules which adopt the β″ packing motif (layer A), layers of NH and Λ-Cr(CO) (layer B), layers of (HO)(NH)18-crown-6 (layer C), and layers of NH and Δ-Cr(CO) (layer D) which produce a superstructure with a repeating pattern of ABCDABCDA. As a result of this packing arrangement, this is the 2D superconductor with the widest gap between conducting layers where only a single donor packing motif is present (β″). Superconducting critical temperatures at ambient pressure observed by electrical transport and magnetic measurements are 4.0-4.9 and 2.5 K, respectively. The strong 2D nature of this system, the broad transition to T at 1.8K, and the transition of α of V ∝ I from 1 to 3 on I-V curves strongly suggest that the superconducting transition is very close to a Kosterlitz-Thouless transition. The magnetic field dependence of the superconducting critical temperature parallel to the conducting plane gives an upper critical field μH > 8 T, which is over the calculated Pauli-Clogston limit for this material.