Influence of substrates on epitaxial thin films of high-temperature superconductors

For growth of high-quality epitaxial thin films of high-temperature superco nductors (HTSCs), it is essential to choose appropriate substrates. For a t hin film of La2-xMxCuO4 (M = Ba, Sr), the superconducting transition temper ature (T-c) is modified by the strain due to the lattice mismatch between t he film and the substrate-For the compressively strained (001) films of La2 -xSrxCuO4 and La2-xBaxCuO4 on LaSrAlO4 substrates, T-c reached 44 and 47 K, respectively, which are higher than the values for bulk samples. Moreover, the T-c-x phase diagrams for the compressed films did not show a local min imum at x similar to 0.125, the so-called "1/8 anomaly". Based on the exper imental results, we suggest that the reduction of antiferromagnetic spin fl uctuation increases T-c in HTSCs. For thin films of Bi2Sr2-CaCu2O8, we foun d that substrates with a small lattice mismatch are very effective in attai ning a smooth and almost precipitate-ftee surface. (C) 2001 Elsevier Scienc e B.V. All rights reserved.