Fermi surface and critical field of YBCO

Abstract We have measured extremal areas of the Fermi surface of YBa 2 Cu 3 O 6.97 by the de Haas-van Alphen effect and the superconducting critical field H c 2 ( T ) by resistence measurements on epitaxial thin of films YBa 2 Cu 3 O 7 (both called YBCO). Magnetic fields up to 140T were used in flux compression experiments. We have tentatively identified another piece of the Fermi surface with an area of 22kT, which is larger than expected. By both the de Haas-van Alphen effect and the resistance measurements, H c 2 with the applied magnetic field H parallel to the c axis of the YBCO is near 130 T. For H perpendicular to the c axis H c 2 is of the order of 900 T.