Kim Sung, Shin Dong Hee, Kim Ju Hwan, Jang Chan Wook, Park Jun Woo, Lee Hosun, Choi Suk-Ho, Kim Seung Hyun, Yee Ki-Ju, Bansal Namrata, Oh Seongshik
Department of Applied Physics and Institute of Natural Sciences, Kyung Hee University, Yongin 446-701, Korea.
Nanotechnology. 2016 Jan 29;27(4):045705. doi: 10.1088/0957-4484/27/4/045705. Epub 2015 Dec 14.
Resonance effects in the thickness-dependent ultrafast carrier and phonon dynamics of topological insulator Bi2Se3 are found irrespective of the kind of substrate by measuring thickness-dependent abrupt changes of pump-probe differential-reflectivity signals (ΔR/R) from Bi2Se3 thin films on four different substrates of poly- and single-crystalline (sc-) ZnO, sc-GaN and SiO2. The absolute peak intensity of the ΔR/R is maximized at ∼t C (6 ∼ 9 quintuple layers), which is not directly related to but is very close to the critical thickness below which the energy gap opens. The intensities of the two phonon modes deduced from the oscillatory behaviors superimposed on the ΔR/R profiles are also peaked at ∼t C for the four kinds of substrates, consistent with the thickness-dependent Raman-scattering behaviors. These resonant effects and others are discussed based on possible physical mechanisms including the effects of three-dimensional carrier depletion and intersurface coupling.
通过测量在多晶和单晶ZnO、单晶GaN和SiO₂这四种不同衬底上的Bi₂Se₃薄膜的泵浦-探测差分反射率信号（ΔR/R）随厚度的突变，发现拓扑绝缘体Bi₂Se₃中与厚度相关的超快载流子和声子动力学存在共振效应，且与衬底种类无关。ΔR/R的绝对峰值强度在约t C（6至9个五重层）处达到最大值，这与能隙打开的临界厚度没有直接关系，但非常接近。从叠加在ΔR/R曲线上的振荡行为推导出的两种声子模式的强度，对于这四种衬底在约t C处也达到峰值，这与厚度相关的拉曼散射行为一致。基于包括三维载流子耗尽和表面间耦合效应在内的可能物理机制，对这些共振效应及其他效应进行了讨论。
