Thickness dependence of superconductivity and resistivity in La1.85Sr0.15CuO4 films

The temperature dependence of resistivity was measured for (0 0 1), (1 0 0) and (1 1 0)-oriented La1.85Sr0.15Cu4 (LSCO) thin films with thickness between 1 and 90 nm on LaSrAlO4 (LSAO) substrates. As thickness increases, superconductivity appears for (0 0 1) films at 3 nm, whereas it appears for (1 0 0) and (1 1 0) films at 23 nm. The difference is explained by compressive strain in the c-axis direction for (1 0 0) and (1 1 0) films caused by a smaller c-axis length in LSAO than in LSCO. It is suggested that small lengths of Cu–O bonds perpendicular to CuO2 planes degrade superconductivity in this system.