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)Cu 2O 3+δ grown by molecular 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 SrCu 2O 3 compounds show localization in agreement with variable range hopping, while some CaCu 2O 3 ladders are metallic for T>150K and show localization below 150K. The conductivity of CaCu 2O 3 increases with charge transfer. It increases more steeply if more than 0.2 hole per copper are transferred.