Vibrational properties and ultrafast photocarrier dynamics of 2H–TaS2 under pressures are studied by the experiments of Raman scattering and femtosecond time resolved spectroscopy. With increasing pressure, the linewidth of two-phonon Raman mode broadens, especially features with a sudden rapid increase above 10 GPa. Meanwhile, the ultrafast dynamics show that the fast decay through optical phonon scattering is significantly suppressed in amplitude and prolonged in lifetime; however, the weight of the slow decay component originating from acoustic phonon scattering is enhanced at high pressures. Furthermore, the electron-phonon (e-ph) coupling constant, λq, and the density of states (DOS) near the Fermi level, N(0), are evaluated qualitatively, which reveals a drastic decrease in e-ph coupling strength and a sudden increase in the DOS beyond 10 GPa. This turning pressure is consistent with the critical point where T c of superconductivity peaks while the charge density wave (CDW) vanishes, indicating the direct correlations between λq, N(0), superconductivity, and the CDW under pressure. The anomaly of the DOS may imply the occurrence of a topological transition of the electronic structure. Our work not only provides valuable information for the understanding of competition between the CDW and superconductivity in 2H–TaS2 but also may open up a routine to unveil the pressure-induced electronic topological transition.

中文翻译：

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压力对 2H-TaS2 中晶格振动和超快光载流子动力学的影响

通过拉曼散射和飞秒时间分辨光谱实验研究了压力下 2H-TaS2 的振动特性和超快光载流子动力学。随着压力的增加，双声子拉曼模式的线宽变宽，特别是在 10 GPa 以上突然快速增加的特征。同时，超快动力学表明，通过光声子散射的快速衰减在幅度上得到显着抑制，寿命得到延长；然而，源自声学声子散射的缓慢衰减分量的权重在高压下会增强。此外，电子-声子 (e-ph) 耦合常数 λq 和费米能级附近的态密度 (DOS) N(0) 被定性评估，这表明 e-ph 耦合强度急剧下降，DOS 突然增加超过 10 GPa。该转向压力与超导 T c 达到峰值而电荷密度波 (CDW) 消失的临界点一致，表明 λq、N(0)、超导和压力下的 CDW 之间存在直接相关性。DOS 的异常可能意味着电子结构的拓扑跃迁的发生。我们的工作不仅为理解 2H-TaS2 中 CDW 与超导性之间的竞争提供了有价值的信息，而且还可能为揭示压力诱导的电子拓扑跃迁开辟道路。表明 λq、N(0)、超导性和压力下的 CDW 之间的直接相关性。DOS 的异常可能意味着电子结构的拓扑跃迁的发生。我们的工作不仅为理解 2H-TaS2 中 CDW 与超导性之间的竞争提供了有价值的信息，而且还可能为揭示压力诱导的电子拓扑跃迁开辟道路。表明 λq、N(0)、超导性和压力下的 CDW 之间的直接相关性。DOS 的异常可能意味着电子结构的拓扑跃迁的发生。我们的工作不仅为理解 2H-TaS2 中 CDW 与超导性之间的竞争提供了有价值的信息，而且还可能为揭示压力诱导的电子拓扑跃迁开辟道路。