INPLANE PRESSURE EFFECT IN STRAINED YBA2CU3O7/LA1.85SR0.15CUO4 SUPERLATTICES

Superconducting strained superlattices have been formed by epitaxial stacking along the c axes of two kinds of unit layers, YBa2Cu3O7 (YBCO) and La1.85Sr0.15CuO4 (LSCO). In these superlattices, the ab plane of YBCO is compressed and the c axis is elongated due to the LSCO layer, which has smaller lattice constant a than that of the YBCO layer. When the thickness of the YBCO layer is reduced, the superconducting transition temperature (T(cend) of YBCO gradually decreases. The decrease of T(c) is, however, much smaller in this system than that in YBa2Cu3O7/PrBa2Cu3O7 and YBa2Cu3O7/(Nd,Ce)2CuO4 superlattices. The T(cend) for only two units (2.4 nm) of the YBCO layers is as high as 72 K. The correlation between the T(c) and the in-plane strain along the a, b axes suggests that the effect of pressure in changing the Cu-O bond length along the CuO2 plane of the superconducting YBCO layer is one of the important factors in raising the T(c) value.