A new molecular superconductor β′-Et2Me2P[Pd(dmit)2]2 (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate)

The anion radical salt beta'-Et2Me2P[Pd(dmit)(2)](2) is non-metallic at ambient pressure. An application of pressure induces a metallic behavior and the system exhibits a superconducting transition in the pressure region of 6.9-10.4 kbar with T-c = 4.0-1.8 K (onset). Under higher pressure, however, non-metallic behavior appears in the low-temperature region. The isostructural salt beta'-Et2Me2Sb[Pd(dmit)(2)](2) also shows pressure-induced metallic behavior. However, not a superconducting transition above 1.6 K, nor a high-pressure non-metallic behavior is observed at pressures up to 16.4 kbar. These Pd(dmit)(2) salts can be characterized by an existence of two different types of bands near the Fermi level. The counter cation dependence of the electronic state under pressure suggests that dimensionality of the electronic structure plays an important role. (C) 1998 Elsevier Science Ltd.