Abstract
We have studied the thickness (t) dependence of the critical-current density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of epitaxial YBCO films grown by fluorine-free MOD to understand the origin of strong depletion of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> by film thickening. We have grown more than thirty samples with t varied from 0.2 to 1.4 μm, and obtained a detailed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -vs-t relation with good statistics. It was found that <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is strongly suppressed by increasing t, and the rate of suppression is changed at around t=0.4 μm. Numerical fitting of the data revealed that the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -t curve above 0.4 μm is well reproduced by a t-inverse-type function. We discuss implications of these observations comparing with cross-sectional TEM results, which show a characteristic vertical distribution of microstructural disorder. This study is based on a half-photolytic F-free MOD process using a uv-excimer lamp which we have recently developed for fabrication of micron-order-thick epitaxial YBCO films.
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