近日，复旦大学的张宗芝及其研究小组与南京大学的王学锋等人合作并取得一项新进展。经过不懈努力，他们利用螺旋度相关超快光激发揭示迪拉克半金属PtTe₂薄膜中的各向异性声子动力学。相关研究成果已于2024年8月1日在国际知名学术期刊《光：科学与应用》上发表。

该研究团队利用超快光泵浦探测光谱技术，展示了相干光学声子（COP）在狄拉克半金属PtTe₂薄膜中的能量转移过程。具体而言，依赖于螺旋度的光驱动产生的各向异性COP信号，揭示了它们与光激发的各向异性自旋极化电子之间通过角动量传递的直接联系。

此外，研究人员还观察到，随着温度的上升，COP的振荡频率和衰减速率分别因COP耗散过程中的非谐波声子-声子散射和电子-声子散射而显著降低。这一研究为揭示狄拉克半金属中相干声子在光电子学和光自旋电子学领域的潜在应用铺平了道路。

据悉，相干声子由于具有反射和控制物质物理性质的非凡能力，在凝聚态物理学中引起了相当大的关注。然而，对拓扑系统内相干声子与其他微观粒子在超快时间尺度上的相互作用的研究仍然是一个活跃而未解决的领域。

附：英文原文

Title: Anisotropic phonon dynamics in Dirac semimetal PtTe2 thin films enabled by helicity-dependent ultrafast light excitation

Author: Li, Ziyang, Chen, Yequan, Song, Anke, Zhang, Jinzhong, Zhang, Rong, Zhang, Zongzhi, Wang, Xuefeng

Issue&Volume: 2024-08-01

Abstract: Coherent phonons have aroused considerable attention in condensed matter physics owing to their extraordinary capacity of reflecting and controlling the physical properties of matter. However, the investigation on the interaction between coherent phonons and other microscopic particles on the ultrafast timescale within topological systems continues to be an active and unresolved area. Here, we show the energy transfer of coherent optical phonons (COP) in Dirac semimetal PtTe₂ thin films using ultrafast optical pump-probe spectroscopy. Specifically, the helicity-dependent light-driven anisotropic COP signals disclose their direct connection with the light-excited anisotropic spin-polarized electrons via an angular momentum transfer. Furthermore, we observe the notable decreases in the COP oscillation frequency and the decay rate with increasing temperatures due to the anharmonic phonon-phonon scattering and electron-phonon scattering in the COP dissipation process, respectively. Our work paves the way for uncovering the coherent phonons in Dirac semimetals for the potential applications in optoelectronics and opto-spintronics.

DOI: 10.1038/s41377-024-01540-z

Source: https://www.nature.com/articles/s41377-024-01540-z