Science Advances ( IF 13.6 ) Pub Date : 2020-03-20 , DOI: 10.1126/sciadv.aaz5015 S. Ito, M. Arita, J. Haruyama, B. Feng, W.-C. Chen, H. Namatame, M. Taniguchi, C.-M. Cheng, G. Bian, S.-J. Tang, T.-C. Chiang, O. Sugino, F. Komori, I. Matsuda
The emergence of quantization at the nanoscale, the quantum size effect (QSE), allows flexible control of matter and is a rich source of advanced functionalities. A QSE-induced transition into an insulating phase in semimetallic nanofilms was predicted for bismuth a half-century ago and has regained new interest with regard to its surface states exhibiting nontrivial electronic topology. Here, we reveal an unexpected mechanism of the transition by high-resolution angle-resolved photoelectron spectroscopy combined with theoretical calculations. Anomalous evolution and degeneracy of quantized energy levels indicate that increased Coulomb repulsion from the surface states deforms a quantum confinement potential with decreasing thickness. The potential deformation strongly modulates spatial distributions of quantized wave functions, which leads to acceleration of the transition beyond the original QSE picture. This discovery establishes a complete picture of the long-discussed transition and highlights a new class of size effects dominating nanoscale transport in systems with metallic surface states.
中文翻译:
表面态库仑排斥加速拓扑半金属纳米膜中的金属-绝缘体转变
纳米级量子量化效应(QSE)的出现允许对物质进行灵活控制,并且是高级功能的丰富来源。半个世纪前,人们预测了QSE诱导的半金属纳米薄膜中转变为绝缘相的过程,并且在其表面状态表现出非平凡的电子拓扑结构方面重新引起了人们的兴趣。在这里,我们通过高分辨率角度分辨光电子能谱结合理论计算揭示了一种意想不到的跃迁机理。量子能级的异常演化和简并性表明,来自表面态的库仑斥力的增加使量子约束势能随着厚度的减小而变形。潜在的变形强烈地调节了量化波函数的空间分布,从而加快了转换速度,超越了原始QSE图片。这项发现为人们讨论了很长时间的过渡提供了完整的图像,并突出了一类新的尺寸效应,该尺寸效应主导着具有金属表面态的系统中的纳米级传输。