Meng Ziyuan, Shi Zhijian, Feng Haifeng, Zhang Hongrun, Ren Zhaoying, Du Yi, Cheng Feng, Ge Binghui, Cai Wei, Hao Weichang
School of Physics, Beihang University, Beijing 100191, P. R. China.
Centre of Quantum and Matter Sciences, International Research Institute for Multidisciplinary Science, Beihang University, Beijing 100191, P. R. China.
ACS Appl Mater Interfaces. 2024 Oct 23;16(42):57395-57403. doi: 10.1021/acsami.4c12665. Epub 2024 Oct 9.
Carrier dynamics is crucial in semiconductors, and it determines their conductivity, response time, and overall functionality. In flat bands (FBs), carriers with high effective masses are predicted to host unconventional transport properties. The FBs usually overlap with other trivial energy bands, however, making it difficult to accurately distinguish their carrier dynamics. In this paper, we have investigated the flat-band carrier dynamics of excited electrons in NbCl, which hosts ideal nonoverlapping FBs near the Fermi level. The optical transition between Hubbard bands is abnormally weakened, exhibiting weak interband absorption and its related slow photoresponse with a time constant of ∼120 s, which are associated with flat-band Mottness-induced large electron effective mass and parity-forbidden transitions. Besides, the localized states created by chlorine vacancies also act as trapping centers for carriers with a time constant of ∼600 s, which are similar to those of the compact localized states of the FB, making the relaxation behavior even more extraordinary. The presence and impacts of atomic defects are confirmed experimentally and theoretically. This work has revealed the abnormal flat-band carrier dynamics of NbCl, which is essential for understanding the optical, electrical, and thermal transport properties of flat-band materials.
载流子动力学在半导体中至关重要，它决定了半导体的电导率、响应时间和整体功能。在平带（FBs）中，具有高有效质量的载流子预计具有非常规的输运特性。然而，平带通常与其他平凡能带重叠，这使得准确区分其载流子动力学变得困难。在本文中，我们研究了NbCl中受激电子的平带载流子动力学，NbCl在费米能级附近具有理想的非重叠平带。哈伯德带之间的光学跃迁异常减弱，表现出弱的带间吸收及其相关的缓慢光响应，时间常数约为120秒，这与平带莫特性诱导的大电子有效质量和宇称禁戒跃迁有关。此外，由氯空位产生的局域态也作为载流子的俘获中心，时间常数约为600秒，这与平带的紧密局域态相似，使得弛豫行为更加异常。原子缺陷的存在及其影响通过实验和理论得到了证实。这项工作揭示了NbCl异常的平带载流子动力学，这对于理解平带材料的光学、电学和热输运性质至关重要。
