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

Abstract

The anion radical salt β′-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 Tc = 4.0−1.8 K (onset). Under higher pressure, however, non-metallic behavior appears in the low-temperature region. The isostructural salt β′-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.