Transport properties of doped cuprate ladder compounds grown by MBE

Charge transfer was measured by X-ray absorption at the copper L-3 edge in thin films of cuprate ladder compounds (Sr,Ca)Cu2O3+delta grown by molecula r beam epitaxy. Depending on the oxidation process, the charge transfer of the films varies in the range 0.07 to 0.26. Transport properties of the SrC u2O3 compounds show localization in agreement with variable range hopping, while some CaCu2O3 ladders are metallic for T>150K and show localization be low 150K. The conductivity of CaCu2O3 increases with charge transfer. it in creases more steeply if more than 0.2 hole per copper are transferred.