As a 3D topological insulator, bismuth selenide (Bi2Se3) has potential applications for electrically and optically controllable magnetic and optoelectronic devices. How the carriers interact with lattice is important to understand the coupling with its topological phase. It is essential to measure with a time scale smaller than picoseconds for initial interaction. Here we use an X-ray free-electron laser to perform time-resolved diffraction to study ultrafast carrier-induced lattice contractions and interlayer modulations in Bi2Se3 thin films. The lattice contraction depends on the carrier concentration and is followed by an interlayer expansion accompanied by oscillations. Using density functional theory (DFT) and the Lifshitz model, the initial contraction can be explained by van der Waals force modulation of the confined free carrier layers. Band inversion, related to a topological phase transition, is modulated by the expansion of the interlayer distance. These results provide insight into instantaneous topological phases on ultrafast timescales.
@article{arxiv.2103.11601,
title = {Ultrafast carrier-lattice interactions and interlayer modulations of Bi2Se3 by X-ray free electron laser diffraction},
author = {Sungwon Kim and Youngsam Kim and Jaeseung Kim and Sungwook Choi and Kyuseok Yun and Dongjin Kim and Soo Yeon Lim and Sunam Kim and Sae Hwan Chun and Jaeku Park and Intae Eom and Kyung Sook Kim and Tae-Yeong Koo and Yunbo Ou and Ferhat Katmis and Haidan Wen and Anthony Dichiara and Donald Walko and Eric C. Landahl and Hyeonsik Cheong and Eunji Sim and Jagadeesh Moodera and Hyunjung Kim},
journal= {arXiv preprint arXiv:2103.11601},
year = {2021}
}