2H-NbSe$_2$ 中电荷密度波转变的远场太赫兹光谱研究

中文摘要 AI 辅助

电荷密度波（CDW）在2H-NbSe$_2$中的形成会改变低能电子结构，并产生与晶格耦合的集体激发。本文利用反射几何中的远场太赫兹时域光谱（THz-TDS）研究了块体2H-NbSe$_2$单晶在CDW转变温度$T_{\mathrm{CDW}} \approx 33$~K附近的特性。在$T_{\mathrm{CDW}}$以下，THz响应显示出约1.5~THz处显著的高频特征，以及寿命更长的亚THz振荡。这两种响应在升温过程中逐渐减弱，并在CDW转变附近被强烈抑制，支持它们与CDW态相关的结论。通过含时金兹堡-朗道模拟，我们重现了实验THz响应的主要特征，将高频响应主要归因于CDW振幅动力学，而亚THz响应归因于缺陷钉扎的相位动力学。约1.5~THz的特征接近报道的拉曼CDW振幅模频率范围，而晶格自由度的耦合也可能影响其光谱位置。我们还进行了补充的角分辨光电子能谱测量，揭示了跨越转变时近费米能级谱权重的动量选择性重新分布。综合这些结果表明，远场THz光谱为探测块体2H-NbSe$_2$中的集体CDW动力学提供了灵敏的手段。

英文摘要

Charge-density-wave (CDW) formation in 2H-NbSe$_2$ modifies the low-energy electronic structure and gives rise to collective excitations coupled to the lattice. Here, we investigate bulk 2H-NbSe$_2$ single crystals using far-field terahertz time-domain spectroscopy (THz-TDS) in reflection geometry across the CDW transition at $T_{\mathrm{CDW}} \approx 33$~K. Below $T_{\mathrm{CDW}}$, the THz response shows a pronounced high-frequency feature near 1.5~THz together with longer-lived sub-THz oscillations. Both responses progressively weaken upon warming and are strongly suppressed across the CDW transition, supporting their association with the CDW state. Using time-dependent Ginzburg--Landau simulations, we reproduce the main features of the experimental THz response, associating the high-frequency response mainly with CDW amplitude dynamics and the sub-THz response with defect-pinned phase dynamics. The $\sim1.5$~THz feature lies close to the frequency range reported for the Raman CDW amplitude mode, while coupling to lattice degrees of freedom may also influence its spectral position. We also performed complementary angle-resolved photoemission spectroscopy measurements, which reveal momentum-selective redistribution of near-Fermi-level spectral weight across the transition. Together, these results show that far-field THz spectroscopy provides a sensitive probe of collective CDW dynamics in bulk 2H-NbSe$_2$.

发表机构

• CENTERA Labs, Institute of High Pressure Physics, Polish Academy of Sciences（波兰科学院高压物理研究所CENTERA实验室）
• International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences（波兰科学院国际磁顶研究中心物理研究所）
• National Synchrotron Radiation Centre SOLARIS, Jagiellonian University（雅盖隆大学国家同步辐射中心SOLARIS）

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