Investigation of superconducting parameters of hydrogenated organic compound κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br

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We investigate the DC magnetization under a magnetic field perpendicular to the layers of the hydrogenated κ-(BEDT-TTF)2Cu[N(CN)2]Br organic superconductor under slow cooling. The relationship between temperature and the lower critical field Hc1 is established by analyzing the linear M(H) response at a low field. We estimate Hc1(0) = 24.61 ± 1.05 G and we highlight its sensitivity to cooling rate near 80 K. The in-plane London penetration depth λ∥(T) calculated from Hc1(T) via Ginzburg-Landau theory, shows a weak T-dependence at low temperatures, but neither an s-wave nor a d-wave gap fully explains it. The upper critical field Hc2(T) near transition is estimated, yielding Hc2(0) = 10.43 ± 0.92 T. The in-plane coherence length ξ∥(T) deduced, suggests intermediate coupling pair strength, a potential BCS-BEC crossover, and a 2D-3D transition near Tc.