High-temperature interface superconductivity in bilayer copper oxide films by pulsed laser deposition

Abstract

In a seminal work, Gozar et al. reported on the high-temperature interface superconductivity in bilayers of insulating La₂CuO₄ and metallic La_2−xSr_xCuO₄ (x=0.45). An interesting question to address is how general and robust this interface superconductivity is. In the past, the cuprate bilayers were grown in a unique atomic-layer molecular beam epitaxy system, with a Sr doping range of x≤0.47, and the atomically flat interface was thought to be indispensable. Here, we have fabricated bilayers of La₂CuO₄ and La_2−xSr_xCuO₄ by pulsed laser deposition. We have tried to extend the nominal doping range of Sr from the previous maximum of 0.47 to the present 1.70 (the nominal Sr content in the targets). X-ray diffraction result indicates that our La_2−xSr_xCuO₄ films with x≤0.60 have very high crystalline quality; but the film crystalline structure degrades gradually with further increasing x, and finally the structure is fully lost when x reaches 1.40 and higher. Although the film quality scatters dramatically, our experiments show that there exists superconductivity for bilayers in nearly the entire over-doped Sr range, except for a non-superconducting region at x∼0.80. These observations demonstrate that the interface superconductivity in copper oxides is very general and robust.

摘要

在2008年发表的一篇经典工作中, Gozar等人报道了由绝缘 性的La₂CuO₄和金属性的La_1.55Sr_0.45CuO₄双层薄膜构成的体系存在 界面超导. 一个重要的有待回答的问题是该界面超导是否强健以 及具有普遍性. 在Gozar等人的工作中, 铜氧化物双层结构是利用 特制的氧化物分子束外延设备生长的, 最大Sr掺杂量仅为0.47. 在 本工作中, 我们首次利用脉冲激光沉积法制备了铜氧化物双层结 构, 并重复出了上述界面超导工作. 在此基础上, 我们将Sr的掺杂 范围大幅扩展到1.70, 结果表明在由La₂CuO₄ 和过掺杂的 La_2−xSr_xCuO₄构成的双层结构中界面超导非常强健和普遍. 值得一 提的是, 我们发现在x>0.8范围内存在一个新的界面超导区间.