论文标题
超快电荷载体和激子动力学中的激子绝缘子通过时间分辨光发射光谱探测
Ultrafast charge carrier and exciton dynamics in an excitonic insulator probed by time-resolved photoemission spectroscopy
论文作者
论文摘要
预期激发型绝缘体相将来自半导体中电子孔对（激子）的自发形成，其中激子结合能超过了电子带隙的大小。在低温下，这些基态激子通过低于Valence带顶部的电子来凝结，从而稳定了新相位，从而扩大了电子带隙。在激子绝缘子系统中探索多个波森现象的设想机会正在引发关于如何在实验中证明基础状态激子的非常积极的争论。在这里，我们采用了一种非平衡方法，从频谱上解散了激子冷凝物的光诱导的动力学，从价带电子的缠绕签名。 By means of time-and angle-resolved photoemission spectroscopy of the occupied and unoccupied electronic states, we follow the complementary dynamics of conduction and valence band electrons in the photoexcited low-temperature phase of Ta2 NiSe5 , the hitherto most promising single-crystal candidate to undergo a semiconductor-to-excitonic-insulator phase transition.发现光激发的传导电子在小于1 ps的范围内放松。它们的放松时间与它们的多余能量成反比，这是我们归因于库仑相互作用减少和TA2Nise5的低维度的依赖性。 （> 10 ps）很久以后，传导带已经清空，费米能以下的光发射强度尚未完全恢复平衡值。值得注意的是，这种看似的载体不平衡不能仅仅通过放松在半导体带隙上的光激发电子和孔的放松来合理化。 [...]
An excitonic insulator phase is expected to arise from the spontaneous formation of electron-hole pairs (excitons) in semiconductors where the exciton binding energy exceeds the size of the electronic band gap. At low temperature, these ground state excitons stabilize a new phase by condensing at lower energy than the electrons at the valence band top, thereby widening the electronic band gap. The envisioned opportunity to explore many-boson phenomena in an excitonic insulator system is triggering a very active debate on how ground state excitons can be experimentally evidenced. Here, we employ a nonequilibrium approach to spectrally disentangle the photoinduced dynamics of an exciton condensate from the entwined signature of the valence band electrons. By means of time-and angle-resolved photoemission spectroscopy of the occupied and unoccupied electronic states, we follow the complementary dynamics of conduction and valence band electrons in the photoexcited low-temperature phase of Ta2 NiSe5 , the hitherto most promising single-crystal candidate to undergo a semiconductor-to-excitonic-insulator phase transition. The photoexcited conduction electrons are found to relax within less than 1 ps. Their relaxation time is inversely proportional to their excess energy, a dependence that we attribute to the reduced screening of Coulomb interaction and the low dimensionality of Ta2NiSe5 . Long after (> 10 ps) the conduction band has emptied, the photoemission intensity below the Fermi energy has not fully recovered the equilibrium value. Notably, this seeming carrier imbalance cannot be rationalized simply by the relaxation of photoexcited electrons and holes across the semiconducting band gap. [...]
