Coexistence of superconductivity with CDW (or SDW): ambient-pressure superconductor based on Ni(dmit)2, α-EDT-TTF[Ni(dmit)2]

We present experimental evidences showing coexistence of superconductivity with CDW (or SDW) in α-EDT-TTF[Ni(dmit)2], a new ambient-pressure superconductor with donor-acceptor structure. The electrical resistance of this salt exhibits a hump around 10∼14 K and drops at 1.3 K due to the superconducting transition. Based on the electrical anisotropy derived from reflectance spectra and weak-field magnetoresistance, this resistance hump is assigned to the CDW (or SDW) formation within EDT-TTF chain. Above 20 K both EDT-TTF and Ni(dmit)2 chain contribute to the electrical conduction, while below 10 K electrical conduction is mainly through Ni(dmit)2 chain. Temperature-pressure phase diagram determined by resistance measurements under pressure is presented.