SUPERCONDUCTIVITY OF STRAINED YBA2CU3O7/(LA1-XSRX)2CUO4 SUPERLATTICES

We have formed three kinds of YBa2Cu3O7-based superconducting superlattices with different carrier concentration and different strain. These superlattices are YBa2Cu3O7 (a=3.88 angstrom, b=3.83 angstrom/PrBa2Cu3O7 (a=3.92 angstrom, b=3.86 angstrom), YBa2Cu3O7/La1.85Sr0.15CuO4 (a=b=3.78 angstrom) and YBa2Cu3O7/La2CuO4 (a=3.82 angstrom, b=3.79 angstrom). The lengths of the a- and b-axes in the YBCO layer can be controlled by changing the neighboring layers. When the thickness of the YBCO layer decreases, the YBCO/PBCO superlattice shows large T(c) deterioration, while the YBCO/LSCO or LCO superlattices with compressed ab-plane show smaller T(c) deterioration for thickness larger than 36 angstrom (3 unit cells). This tendency is independent of carrier concentration of the neighboring layer. When the thickness is below 36 angstrom, YBCO/LSCO shows higher T(c) than YBCO/LCO, although the strain is the same for both superlattices. These behaviors suggest that the in-plane stress along the ab-axis is important to control the T(c) value, and the hole filling effect is also important for ultra-thin films.