Metal-insulator transitions and singlet polarons in one-dimensional Ca2+xY2-xCu5O10

One-dimensional dopable Ca(2+x)Y(2-x)Cu(5)O(10) is characterized by the presence of Zhang-Rice singlets (ZRSs) in the electronic ground state and a series of magnetic and metal-insulating phase transitions. With the use of unconventional first-principles calculations suited to the study of strongly correlated materials, we describe the change in the electronic and magnetic properties through the whole doping range (up to one hole per CuO(2) unit). Singlet polarons, whose space and energy distributions are described in detail, are found by our calculations to be stable above a concentration of similar to 0.3 holes per Cu. We give a sound interpretation of the observed insulating behavior and loss of antiferromagnetic ordering at low doping and predict unusual properties in the doping region, where experimental data are not yet available. The system is antiferromagnetic and hopping conducting for x/n up to about 0.25, gapped around 0.3-0.4, metallic from 0.4 to 1, and gapped and ZRS-saturated at x/n=1.