Dynamic scaling analyses of the ac conductivity measured between 1 and 190 kOe before and after heavy ion irradiation parallel to the c axis reveal continuous phase transitions to superconducting glassy vortex states. A first unambiguous evidence for the predicted Bose-glass (BG) behavior being stable up to the matching field H f 40 kOe is presented. The critical exponents differ significantly from those obtained for HЌc and those reported recently for twin-free crystals, suggesting that the inherent uncorrelated disorder in thin films reduces the vortex line wandering, and therefore enhances the BG transition.

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Epitaxial CeO2 buffer layers and YBa2Cu3O7−δ thin films have been grown in situ on (11̄02) sapphire by electron beam evaporation. Buffer layers of only 20 nm thickness inhibit interdiffusion between YBa2Cu3O7−δ and Al2O3 as determined by depth profiling using x-ray photoelectron spectroscopy. The layers show smooth surfaces and narrow interfaces. High lattice perfection of the CeO2 layer has been shown by x-ray diffraction. Laue oscillations up to ninth order have been observed in thin CeO2 buffer layers on sapphire. We found only one epitaxial orientation with YBa2Cu3O7−δ (001) ∥ CeO2 (001) ∥ Al2O3 (11̄02) and YBa2Cu3O7−δ [110] ∥ CeO2 [100] ∥ Al2O3 [112̄0]. YBa2Cu3O7−δ films grown on these buffer layers reveal Tc=88±0.5 K, ρ(300 K)=380 μΩ cm, and jc(77 K, 0 T)=1.3×106 A/cm2.

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