Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T‐TaSe2
Spectrally Resolving the Phase and Amplitude of Coherent Phonons in the Charge Density Wave State of 1T‐TaSe2
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DOI：
10.1002/adom.202200362
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发表时间：
2022-05
影响因子：
9
通讯作者：
C. Sayers;S. Dal Conte;D. Wolverson;C. Gadermaier;G. Cerullo;E. Carpene;E. da Como
中科院分区：
文献类型：
--
作者：
C. Sayers;S. Dal Conte;D. Wolverson;C. Gadermaier;G. Cerullo;E. Carpene;E. da Como
相干声子的激发和检测为凝聚态物质的研究提供了独特的视角，特别是对于具有强电子-声子耦合的材料。在层状电荷密度波（CDW）化合物1 T-TaSe 2中，使用瞬态宽带反射率光谱进行了相干声子的研究，光子能量范围为1.75-2.65 eV。几个强烈的和持久的（>20 ps）振荡，所产生的CDW超晶格重建，观察允许详细分析其振幅和相位的光谱依赖性。对于高于2.4 eV的能量，其中跃迁涉及Ta d带，发现在2.19 THz处的CDW振幅模式主导相干响应。相反，在较低的能量下，在额外的频率之间会出现跳动，在2.95 THz处有一个特别强烈的模式。有趣的是，光谱分析揭示了在2.4 eV处的π相移。结果进行了讨论，考虑到特定模式的选择性耦合的能带中看到的稳态反射率的光学跃迁。这项工作展示了相干声子光谱如何区分和分辨与CDW阶强耦合的光学状态，并提供通常隐藏在传统稳态技术中的额外信息。
The excitation and detection of coherent phonons have given unique insights into the condensed matter, in particular for materials with strong electron–phonon coupling. A study of coherent phonons is reported in the layered charge density wave (CDW) compound 1T‐TaSe2 performed using transient broadband reflectivity spectroscopy, in the photon energy range 1.75–2.65 eV. Several intense and long‐lasting (>20 ps) oscillations, arising from the CDW superlattice reconstruction, are observed allowing for detailed analysis of the spectral dependence of their amplitude and phase. For energies above 2.4 eV, where transitions involve Ta d‐bands, the CDW amplitude mode at 2.19 THz is found to dominate the coherent response. At lower energies, instead, beating arises between additional frequencies, with a particularly intense mode at 2.95 THz. Interestingly, the spectral analysis reveals a π phase shift at 2.4 eV. Results are discussed considering the selective coupling of specific modes to energy bands involved in the optical transitions seen in steady‐state reflectivity. The work demonstrates how coherent phonon spectroscopy can distinguish and resolve optical states strongly coupled to the CDW order and provide additional information normally hidden in conventional steady‐state techniques.