Weis M, Wilk B, Vaudel G, Balin K, Rapacz R, Bulou A, Arnaud B, Szade J, Ruello P
A. Chelkowski Institute of Physics and Silesian Center for Education and Interdisciplinary Research,75 Pulku Piechoty 1A University of Silesia, 41-500, Chorzów, Poland.
Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, 72085 Le, Mans, France.
Sci Rep. 2017 Oct 23;7(1):13782. doi: 10.1038/s41598-017-12920-4.
Heralded as one of the key elements for next generation spintronics devices, topological insulators (TIs) are now step by step envisioned as nanodevices like charge-to-spin current conversion or as Dirac fermions based nanometer Schottky diode for example. However, reduced to few nanometers, TIs layers exhibit a profound modification of the electronic structure and the consequence of this quantum size effect on the fundamental carriers and phonons ultrafast dynamics has been poorly investigated so far. Here, thanks to a complete study of a set of high quality molecular beam epitaxy grown nanolayers, we report the existence of a critical thickness of around ~6 nm, below which a spectacular reduction of the carrier relaxation time by a factor of ten is found in comparison to bulk Bi Te In addition, we also evidence an A1g optical phonon mode softening together with the appearance of a thickness dependence of the photoinduced coherent acoustic phonons signals. This drastic evolution of the carriers and phonons dynamics might be due an important electron-phonon coupling evolution due to the quantum confinement. These properties have to be taken into account for future TIs-based spintronic devices.
拓扑绝缘体（TIs）被誉为下一代自旋电子器件的关键要素之一，如今正逐步被设想为诸如电荷到自旋电流转换之类的纳米器件，或者例如基于狄拉克费米子的纳米肖特基二极管。然而，当缩减到几纳米时，TI层的电子结构会出现深刻变化，而到目前为止，这种量子尺寸效应在基本载流子和声子超快动力学方面的影响尚未得到充分研究。在此，通过对一组高质量分子束外延生长的纳米层进行全面研究，我们报告了存在一个约6纳米左右的临界厚度，低于此厚度时，与体相Bi Te相比，载流子弛豫时间会显著缩短一个数量级。此外，我们还证明了A1g光学声子模式软化以及光致相干声子信号出现厚度依赖性。载流子和声子动力学的这种剧烈演变可能是由于量子限制导致的重要电子 - 声子耦合演变。对于未来基于TI的自旋电子器件，必须考虑这些特性。
