An Investigation of the Influence of a Magnetic Field on the Chemical Potential of Electrons in Superconducting YBCO Thin Films

It is shown that measurements of the chemical potential variation in a magnetic field could give valuable information about the magnetisation of thin films. Oscillations of mu in YBCO single crystal films evaporated on cleaved MgO substrates were observed. These oscillations may be ascribed either to the de Haas - van Alphen effect or to mesoscopic effects arising due to weak link currents. Large changes of mu resulting from superconducting shielding currents were observed in films evaporated on polished substrates. For films deposited on polished NdGaO3 substrate the change of mu was mainly reversible. For films deposited on polished MgO, SrTiO3 and LaAlO3 substrates mu changed irreversibly.