Han Yadong, Yu Junhong, Zhang Hang, Xu Fang, Peng Kunlin, Zhou Xiaoyuan, Qiao Liang, Misochko Oleg V, Nakamura Kazutaka G, Vanacore Giovanni M, Hu Jianbo
State Key Laboratory for Environment-Friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, China.
Laboratory for Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, 621900, China.
J Phys Chem Lett. 2022 Jan 20;13(2):442-448. doi: 10.1021/acs.jpclett.1c03704. Epub 2022 Jan 6.
Layered tin selenide (SnSe) has recently emerged as a high-performance thermoelectric material with the current record for the figure of merit () observed in the high-temperature phase. So far, access to the phase has been mainly obtained via thermal equilibrium methods based on sample heating or application of external pressure, thus restricting the current understanding only to ground-state conditions. Here, we investigate the ultrafast carrier and phononic dynamics in SnSe. Our results demonstrate that optical excitations can transiently switch the point-group symmetry of the crystal from to at room temperature in a few hundreds of femtoseconds with an ultralow threshold for the excitation carrier density. This nonequilibrium phase is found to be driven by the displacive excitation of coherent A phonons and, given the absence of low-energy thermal phonons, exists in SnSe with the status of 'cold lattice with hot carriers'. Our findings provide an important insight for understanding the nonequilibrium thermoelectric properties of SnSe.
层状硒化锡（SnSe）最近已成为一种高性能热电材料，在高温相中的优值（）创下了当前记录。到目前为止，获得相主要是通过基于样品加热或施加外部压力的热平衡方法，因此目前的认识仅限于基态条件。在这里，我们研究了SnSe中的超快载流子和声子动力学。我们的结果表明，光激发可以在室温下在几百飞秒内以超低的激发载流子密度阈值将晶体的点群对称性从瞬态切换到。发现这种非平衡相是由相干A声子的位移激发驱动的，并且由于不存在低能热声子，在SnSe中以“热载流子冷晶格”的状态存在。我们的发现为理解SnSe的非平衡热电性质提供了重要的见解。
