Preparation and Properties of Organic Superconductor κ-(Bedt-TTF)2 [Cu(NCS)2] and Its Related Materials

Abstract

ABSTRACTκ-(BEDT-TTF)2 [Cu(NCS)2] has a two-dimensional (2D) layered structure. The compound is metallic with the room temperature conductivity of 10–40 S/cm within the 2D plane but showed a semiconductive-like anomaly between 270 and 90K. The superconducting transition was observed at Tc=10.4K and Tc increased by 10% on the sample of deuterated BEDT-TTF (Tc=11.4K). The upper critical field, Hc2, was more than 20 Tesla below 2K within the 2D plane which is more than the expected value from the simple BCS theory. The transport critical current density was estimated as 100 A/cm2 (5.1K, 0 Tesla, l//b, H//c) which is an order of magnitude smaller than that obtained from the magnetization curve hysteresis. 1H-NMR showed a big enhancement of the relaxation rate well below Tc. The tunneling spectra showed anisotropic gap and the magnetic field penetration depth measurements strongly suggest that this system is a gapless superconductor. (BEDT-TTF)2[KHg(SCN)4] is an organic metal and showed both Shubnikov-de Haas effect and angle-dependent quantum oscillation indicating that this system has a warped 2D Fermi surface.