用STM研究薄膜锰氧化物表面形态与电子结构之间的相关性
Correlations between the morphology and the electronic structure at the surface of thin film manganites, investigated with STM
摘要：
薄膜巨磁电阻锰氧化物如La $_{0.67}$ Ca $_{0.33}$ MnO $_{3}$（LCMO）已经被深入研究了十多年，但是可能的纳米级电子相分离的问题还没有完全解决。扫描隧道显微镜/光谱学（STS）在研究相分离中一直是关键的，但受到表面敏感而不是体积敏感的阻碍。对于我们的溅射LCMO薄膜的数据表明表面形态和相分离的签名之间的强相关性;粗糙的薄膜显示相分离，而原子级平坦的薄膜是电子均匀的，但有一个或多或少的非活性表面层。无论表面形态如何，膜体都是电子和磁活性的。许多关于STS测量的电子不均匀性的报告结论被这个问题所混淆。我们研究了应变和无应变的薄膜，并发现基板引起的应变和电子相分离或死层之间没有相关性。
英文摘要：
Thin-film colossal magnetoresistance manganites such as La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) have now been intensely studied for more than a decade, but the issue of possible nanoscale electronic phase separation is not fully solved. Scanning Tunneling Microscopy / Spectroscopy (STS) has been pivotal in studying phase separation, but is hindered by being surface- rather than bulk-sensitive. For our sputtered LCMO films the data indicates a strong correlation between surface morphology and signatures of phase separation; rough films show phase separation while atomically flat films are electronically homogeneous but have a more or less inactive surface layer. Regardless of surface morphology, the film bulk is electronically and magnetically active. Many of the reported conclusions about electronic inhomogeneities measured by STS have been confused by this issue. We study both strained and unstrained films and find no correlation between substrate-induced strain and either electronic phase separation or dead layers.
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