Effect of adjacent insulating oxide layers on superconductivity of one unit cell thick YBa 2Cu 3O 7-δ layers in PrBa 2Cu 3O 7-δ/YBa 2Cu 3O 7-δ/insulating oxide trilayers
Abstract
One unit cell thick (1-UCT) YBa 2Cu 3O 7-δ (YBCO) adjacent to nonsuperconducting PrBa 2Cu 3O 7-δ (PrBCO) buffer layers have been grown epitaxially on SrTiO 3 (100) using molecular beam epitaxy (MBE). The layer thickness was accurately controlled by monitoring reflection high-energy electron diffraction (RHEED) specular intensity oscillations. Various oxide caps were grown epitaxially on the 1-UCT YBCO layer to form PrBCO/1-UCT YBCO/insulating oxide trilayers. It was found that superconducting 1-UCT YBCO layers were achieved when BaO with a good lattice match to YBCO was used as an insulating oxide in the trilayers. As the terminating atomic layer of 1-UCT YBCO layer is CuO 1-δ, the addition of an atomic BaO layer means the completion of the charge reservoir block of BaO-CuO 1-δ-BaO positioned above the CuO 2 bilayer (CuO 2YCuO 2). The PrBCO buffer layers provide another charge reservoir block positioned below the CuO 2 bilayer interposing Y. Therefore, the minimum unit for superconductivity in YBCO is the CuO 2 bilayer sandwiched between the charge reservoir blocks. In the present study, the systematic substitution of various AO layers for the one-sided atomic BaO layer of the charge reservoir block has been made by epitaxial growth of cap oxides such as rock-salt-type and perovskite-type oxides on the CuO 1-δ-terminated surface of 1-UCT YBCO layers. It is found that the small lattice mismatch between YBCO and the cap oxides, in addition to divalent A ions such as Ba 2+, Sr 2+, Ca 2+, Pb 2+ and Cd 2+ in atomic AO layers subsequent to the CuO 1-δ-terminated surface, is a requirement for superconductivity in 1-UCT YBCO layers.
- Publication:
-
Journal of Crystal Growth
- Pub Date:
- May 1995
- DOI:
- 10.1016/0022-0248(95)80104-K
- Bibcode:
- 1995JCrGr.150.1074B