Abstract
Very recently BaSrNiO4 was reported to be a Fermi glass (Schilling et al. in J. Phys., Condens. Matter 21:015701, 2009). Its structure is essentially the one of K2NiF4 as is that of La2CuO4, in which the occurrence of high-temperature superconductivity (HTS) upon hole doping was first reported (Bednorz and Müller in Z. Phys.B 64:189, 1986; Adv. Chem. 100:757, 1988). The carriers in both have mainly eg character, and move in a stochastic potential as documented by a number of experiments. The difference of the two behaviors is mainly ascribed to the formation of intersite bipolarons (Kabanov and Mihailovic in J. Supercond. 13:950, 2000) , which is estimated to be up to two orders of magnitude larger in La2CuO4 than in BaSrNiO4. From this it follows that for HTS to occur, a large bipolaron formation energy in layered structures is required
Müller, K A