论文标题
使用瞬态吸收光谱法澄清拓扑绝缘子BI2SE3的超薄膜中的超快载体动力学
Clarifying ultrafast carrier dynamics in ultrathin films of the topological insulator Bi2Se3 using transient absorption spectroscopy
论文作者
论文摘要
拓扑绝缘子BI2SE3中的超快载体动力学最近使用多种技术进行了深入研究。但是，我们没有意识到为这些目的开发瞬态吸收（TA）光谱的任何成功实验。在这里，我们证明，如果将〜730 nm波长泵送（〜1.7 eV光子能）应用于超薄的bi2se3膜，则TA光谱覆盖了整个可见区域，因此明确指出了两光子激发（〜3.4 eV）。发现载体松弛动力学由在散装状态和狄拉克表面状态（SS）中出现的极性声子级联发射（包括SS-Bulk-SS垂直电子传输）所支配，并且还受到越高能量是否呈现Dirac Point的较高能量（〜1.5 ev）SSS（〜1.5 ev）SSS（SSS 2）。我们已经认识到，当狄拉克锥之间的间隙超过极性声音子和共振缺陷时，SS2充当一个阀，从而大大减慢了电子的松弛。通过逆Bremsstrahlung型游离载体吸收，可以检测到散布SS2中电子的逐渐积累。
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.
