1$T$-TaS$_2$中集体电荷激发的动量分辨电子能量损失谱（M-EELS）研究
Momentum-resolved EELS study of collective charge excitations in 1$T$-TaS$_2$
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中文总结 AI 辅助
本研究利用动量分辨电子能量损失谱（M-EELS）探究1$T$-TaS$_2$在近公度到公度电荷密度波相变中的电荷激发，证实M-EELS可同时获取其晶格动力学与电荷激发信息，揭示相变过程中相关物理量的演化。
中文摘要 AI 辅助
我们采用动量分辨电子能量损失谱（M-EELS）研究1$T$-TaS$_2$在近公度到公度电荷密度波（CDW）相变过程中的低能电荷激发。单晶X射线衍射和弹性M-EELS测量证实，进入公度相后CDW波矢发生预期的旋转。在近公度相，低能M-EELS谱显示出声子支和两个光学声子特征，其能量与色散与此前的计算及非弹性X射线测量结果大体一致。相变过程中，光学声子能量几乎保持不变，而在CDW有序波矢附近，其谱强度呈现出显著的温度依赖性。在更高能量下，有限动量电荷响应在相变前后发生了谱重的显著重新分布，这与能隙的打开一致。这些结果表明，M-EELS可同时获取1$T$-TaS$_2$中的晶格动力学和有限动量价带电荷激发信息，揭示了它们在公度CDW相变过程中的演化。
英文摘要
We use momentum-resolved electron energy-loss spectroscopy (M-EELS) to study the low-energy charge excitations of 1$T$-TaS$_2$ across the nearly commensurate-to-commensurate charge-density-wave (CDW) transition. Single-crystal x-ray diffraction and elastic M-EELS measurements confirm the expected rotation of the CDW wave vector upon entering the commensurate phase. In the nearly commensurate phase, the low-energy M-EELS spectra reveal an acoustic phonon branch and two optical phonon features whose energies and dispersions are broadly consistent with previous calculations and inelastic x-ray measurements. Across the transition, the optical phonon energies remain nearly unchanged, while their spectral intensity develops a pronounced temperature dependence near the CDW ordering wave vector. At higher energies, the finite-momentum charge response undergoes a substantial redistribution of spectral weight below the transition, consistent with the opening of an energy gap. These results demonstrate that M-EELS provides simultaneous access to lattice dynamics and finite-momentum valence band charge excitations in 1$T$-TaS$_2$, revealing their evolution across the commensurate CDW transition.
