Fang Shaoyin, Zhu Ruidan, Lai Tianshu
State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-Sen University, Guangzhou, 510275, P.R. China.
Sci Rep. 2017 Mar 21;7(1):287. doi: 10.1038/s41598-017-00396-1.
Spin relaxation dynamics of holes in intrinsic GaAs quantum wells is studied using time-resolved circular dichromatic absorption spectroscopy at room temperature. It is found that ultrafast dynamics is dominated by the cooperative contributions of band filling and many-body effects. The relative contribution of the two effects is opposite in strength for electrons and holes. As a result, transient circular dichromatic differential transmission (TCD-DT) with co- and cross-circularly polarized pump and probe presents different strength at several picosecond delay time. Ultrafast spin relaxation dynamics of excited holes is sensitively reflected in TCD-DT with cross-circularly polarized pump and probe. A model, including coherent artifact, thermalization of nonthermal carriers and the cooperative contribution of band filling and many-body effects, is developed, and used to fit TCD-DT with cross-circularly polarized pump and probe. Spin relaxation time of holes is achieved as a function of excited hole density for the first time at room temperature, and increases with hole density, which disagrees with a theoretical prediction based on EY spin relaxation mechanism, implying that EY mechanism may be not dominant hole spin relaxation mechanism at room temperature, but DP mechanism is dominant possibly.
利用时间分辨圆二色吸收光谱在室温下研究了本征GaAs量子阱中空穴的自旋弛豫动力学。研究发现，超快动力学主要由能带填充和多体效应的协同贡献主导。这两种效应的相对贡献在电子和空穴的强度上是相反的。因此，具有同向和交叉圆偏振泵浦和探测的瞬态圆二色性微分透射（TCD-DT）在几个皮秒延迟时间呈现出不同的强度。激发空穴的超快自旋弛豫动力学在具有交叉圆偏振泵浦和探测的TCD-DT中得到了灵敏的反映。建立了一个包括相干伪像、非热载流子热化以及能带填充和多体效应的协同贡献的模型，并用于拟合具有交叉圆偏振泵浦和探测的TCD-DT。首次在室温下获得了空穴自旋弛豫时间作为激发空穴密度的函数，并且随着空穴密度的增加而增加，这与基于EY自旋弛豫机制的理论预测不一致，这意味着EY机制在室温下可能不是主导的空穴自旋弛豫机制，而DP机制可能是主导的。
