Enhancement of the superconducting transition temperature of La2-xSrxCuO4 and La1.875Ba0.125CuO4 bilayers: Bilayer and reference film prepared on the same wafer

Recently, a paper was published by Yuli et al. [Phys. Rev. Lett. 101, 057005 (2008)], in which a large T-c enhancement was reported in bilayers of the nonsuperconducting La1.65Sr0.35CuO4 and superconducting La2-xSrxCuO4 in the underdoped regime, in comparison with the same bare La2-xSrxCuO4 film. This result however, was not reproduced in the present experiments and an effort is made trying to resolve this puzzle. The difference in the present study is that both the bilayer and the bare reference film were prepared in the same deposition run on different parts of the same wafer. This is in contrast to the previous experiments where the bilayers and bare reference films were prepared in different runs and on different wafers. Nevertheless, a small but clear T-c enhancement effect of 1.4-2 K is found in the present study in a similar system of La1.65Sr0.35CuO4-La1.875Ba0.125CuO4 bilayers, which is in line with the theoretical arguments presented previously.