Electrical Resistivity under High Pressure and Upper Critical Magnetic Field of the Molecular Superconductor α-(EDT-TTF)[Ni(dmit)₂]

Abstract

Electrical resistivity under a high pressure and the upper critical magnetic field (H_c2) in the superconducting state were investigated on the ambient-pressure superconductor α -(EDT-TTF)[Ni(dmit)₂], which exhibits a phase transition around 20K and the superconducting transition at 1.3K under ambient pressure. Above 9.9, kbar, the superconducting transition was not observed down to 0.5K, while the former transition survived up to 13.7kbar. The temperature dependence of H_c2 was estimated: |dH_c2/dT|_{T=T_c} ≈ -0.27T/K (Bparallel c^*-axis); |dH_c2/dT|_{T=T_c} ≈ -3.5T/K (B// ab-plane). The anisotropy of H_c2 within the ab-plane was found to be quite small indicating the two-dimensionally isotropic character within the ab-plane in the superconducting state of the salt.