拓扑绝缘体
电子
超快激光光谱学
光子
超短脉冲
材料科学
光谱学
声子
吸收(声学)
带隙
光子能量
放松(心理学)
分子物理学
物理
原子物理学
凝聚态物理
光学
激光器
心理学
社会心理学
量子力学
作者
Yuri D. Glinka,Junzi Li,Tingchao He,Xiao Wei Sun
出处
期刊:ACS Photonics
[American Chemical Society]
日期:2021-04-09
卷期号:8 (4): 1191-1205
被引量:19
标识
DOI:10.1021/acsphotonics.1c00115
摘要
Ultrafast carrier dynamics in the topological insulator Bi2Se3 have recently been intensively studied using a variety of techniques. However, we are not aware of any successful experiments exploiting transient absorption (TA) spectroscopy for these purposes. Here we demonstrate that if the ~730 nm wavelength pumping (~1.7 eV photon energy) is applied to ultrathin Bi2Se3 films, TA spectra cover the entire visible region, thus unambiguously pointing to two-photon excitation (~3.4 eV). The carrier relaxation dynamics is found to be governed by the polar optical phonon cascade emission occurring in both the bulk states and the Dirac surface states (SS), including SS-bulk-SS vertical electron transport and being also exclusively influenced by whether the Dirac point is presented between the Dirac cones of the higher energy (~1.5 eV) Dirac SS (known as SS2). We have recognized that SS2 act as a valve substantially slowing down the relaxation of electrons when the gap between Dirac cones exceeds the polar optical phonon and resonant defects energies. The resulting progressive accumulation of electrons in the gapped SS2 becomes detectable through the inverse bremsstrahlung type free carrier absorption.
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