Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$

Dmitriy Yavorskiy; Adil Rehman; Wojciech Brzezicki; Jan Skolimowski; Marcin Białek; Wojciech Knap; Dawid Wutke; Natalia Olszowska; Andrzej Wiśniewski; Ashutosh S. Wadge

arXiv · 2609.36125

Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$

Dmitriy Yavorskiy·Adil Rehman·Wojciech Brzezicki·Jan Skolimowski·Marcin Białek·Wojciech Knap·Dawid Wutke·Natalia Olszowska·Andrzej Wiśniewski·Ashutosh S. Wadge

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Abstract

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$_2$.

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Dmitriy Yavorskiy, Adil Rehman, Wojciech Brzezicki, Jan Skolimowski, Marcin Białek, Wojciech Knap, Dawid Wutke, Natalia Olszowska, Andrzej Wiśniewski, Ashutosh S. Wadge. 2026-09-28. Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$. https://arxiv.org/abs/2609.36125

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