Polarons, bipolarons, and possible High-Tc superconductivity in metal-ammonia solutions

We examine the nature of fluid metal-ammonia solutions with a special emphasis on the electronic structure and dynamics of polaronic and bipolaronic charge carriers. Importantly, we find that close to the compositionally-induced Nonmetal-to-Metal Transition in the fluid at low temperatures (ca. 240K), the vast majority (ca. 85% or above) of current carriers are highly mobile, diagmagnetic (S = 0) bipolarons. This raises the intriguing possibility, first proposed by R. A. Ogg in 1946, of a Bose-Einstein Condensation (BEC) of trapped electron pairs in vitreous, quenched metal-ammonia solutions. From a "modern" (2000) perspective we believe that there are important similarities to the situation in the crystalline layered cuprates, where we have argued elsewhere that High-T-c superconductivity derives from the BEC of bipolarons in the electronically active CuO2 planes [A. S. Alexandrov and P. P. Edwards, Physica C 331, 97 (2000)]. We now propose that the search begins for high temperature superconductivity in quenched metal-ammonia and related solutions.