Information technology demands high-speed optoelectronic devices, but going beyond the one terahertz (THz) barrier is challenging due to the difficulties associated with generating, detecting, and processing high-frequency signals. Here, we show that femtosecond-laser-driven phonons can be utilized to coherently manipulate the excitonic properties of semiconductors at THz frequencies. The precise control of the pump and subsequent time-delayed broadband probe pulses enables the simultaneous generation and detection processes of both periodic lattice vibrations and their couplings with electronic states. Combining ultralow frequency Raman spectroscopy with first-principles calculations, we identify the unique phonon mode-selective and probe-energy dependent features of electron-phonon interactions in layered PdSe2. Two distinctive types of coherent phonon excitations could couple preferentially to different types of electronic excitations: the intralayer (4.3 THz) mode to carriers and the interlayer (0.35 THz) mode to excitons. This work provides new insights to understand the excited-state phonon interactions of 2D materials, and to achieve future applications of optoelectronic devices operating at THz frequencies.
@article{arxiv.2007.02034,
title = {Phonon-assisted electronic states modulation of few-layer PdSe2 at terahertz frequencies},
author = {Ziqi Li and Bo Peng and Miao-Ling Lin and Yu-Chen Leng and Bin Zhang and Chi Pang and Ping-Heng Tan and Bartomeu Monserrat and Feng Chen},
journal= {arXiv preprint arXiv:2007.02034},
year = {2021}
}