Spin polarons in high-Tc copper oxides: Differences between electron- and hole-doped systems

It is argued that in the small-doping region there is an asymmetry between the hole-doped and the electron-doped copper oxide systems. This asymmetry is reflected in both the magnetic and transport properties. Significant oxygen p-p orbital overlap leads to a large conduction-band width, which has qualitatively different effects on the two differently doped systems. In the hole-doped case, large-spin polarons are formed as the system is doped; this leads to a quick destruction of the antiferromagnetic correlation. In the electron-doped case, doped carriers are more localized; thus the magnetic correlation is more robust with respect to doping. In the low doping concentration, the low-temperature conductivity is shown to be two-dimensional variable-range-hopping type. The conductivity, which is expected to scale with the asymmetry of the magnetic phase diagram, is smaller in an electron-doped system than that of a hole-doped system