用时间分辨光反射率研究本征拓扑绝缘体$\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$的纳秒动力学
Nanosecond dynamics in intrinsic topological insulator $\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$ revealed by time-resolved optical reflectivity
摘要：
$\text{Bi}_2\text{Se}_3$是一种理想的三维拓扑绝缘体，其化学势可以通过锑掺杂进入体带隙。在这里，我们利用超快时间分辨瞬态反射率来表征$\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$纳米片中的光激发载流子衰减。我们报告了在低温下，与$n$型大块金属$\text{Bi}_2\text{Se}_3$相比，大块绝缘$\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$纳米片中的大块载流子弛豫时间显著减慢，这在零泵浦注量极限下接近$3.3 \text{ ns}$。这种长寿命的衰变在不同的能量密度和锑浓度之间是相关的，揭示了$n$型$\text{Bi}_2\text{Se}_3$中不存在的独特衰变动力学，即体载流子的缓慢双分子复合。
英文摘要：
$\text{Bi}_2\text{Se}_3$ is an ideal three-dimensional topological insulator in which the chemical potential can be brought into the bulk band gap with antimony doping. Here, we utilize ultrafast time-resolved transient reflectivity to characterize the photoexcited carrier decay in $\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$ nanoplatelets. We report a substantial slowing of the bulk carrier relaxation time in bulk-insulating $\text{Bi}_{2-x}\text{Sb}_x\text{Se}_3$ nanoplatelets as compared to $n$-type bulk-metallic $\text{Bi}_2\text{Se}_3$ at low temperatures, which approaches $3.3 \text{ ns}$ in the zero pump fluence limit. This long-lived decay is correlated across different fluences and antimony concentrations, revealing unique decay dynamics not present in $n$-type $\text{Bi}_2\text{Se}_3$, namely the slow bimolecular recombination of bulk carriers.
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