Indirect electric field doping of the CuO2 planes of the cuprate   NdBa2Cu3O7 superconductor
  The mechanism of field-effect doping in the "123" high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO2 planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric/HTS interface determine the electric field doping of the CuO2 planes 
M. Salluzzo, G. Ghiringhelli, J. C. Cezar, N. B. Brookes, G. M. De   Luca, F. Fracassi and R. Vaglio