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1. Temperature-dependent polarized Raman scattering in candidate topological superconductor 2M-WS ₂

   https://doi.org/10.1088/2053-1583/ae4760  

   Gautam, Sabin; Ye, Gaihua; Nnokwe, Cynthia; Samuel, John; Hossain, A_K_M Manjur; Wang, Wenyong; Ackerman, John; Leonard, Brian M; Bayne, Stephen B; Tian, Jifa; et al (February 2026, 2D Materials)

   Abstract The monoclinic 2M phase of tungsten disulfide (2M-WS₂) has emerged as a promising platform for topological superconductivity, combining topological surface states, anisotropic thermoelectric response, and superconductivity with a critical temperature of ∼8.8K. A detailed understanding of its electron–phonon coupling and phonon anharmonicity is, however, still lacking. Here, we investigate the phonon properties of few-layer 2M-WS₂as functions of laser power, temperature, polarization, and magnetic field using polarized Raman spectroscopy down to 12.5 K. We uncover an unusual, non-linear temperature dependence of the Raman shifts in selected modes, consistent with strong, mode-dependent electron–phonon interactions that dominate over phonon–phonon scattering at low temperatures. Angle-resolved polarized Raman measurements further reveal a pronounced change in the polarization behavior of the $A_g$ (4) mode at ∼316cm⁻¹upon cooling, indicating a modification of the underlying lattice and electronic anisotropy. In contrast, the applied magnetic field has a negligible influence on the Raman response over the measured temperature range. Together, these results advance the microscopic understanding of vibrational dynamics and electron–phonon coupling in few-layer 2M-WS₂and provide important insight into the lattice-electronic interplay relevant for its unconventional superconductivity and potential quantum and thermoelectric device applications. 

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2. Raman study of layered breathing kagome lattice semiconductor Nb ₃ Cl ₈

   https://doi.org/10.1088/2053-1583/acfa10  

   Jeff, Dylan A; Gonzalez, Favian; Harrison, Kamal; Zhao, Yuzhou; Fernando, Tharindu; Regmi, Sabin; Liu, Zhaoyu; Gutierrez, Humberto R; Neupane, Madhab; Yang, Jihui; et al (September 2023, 2D Materials)

   Abstract Niobium chloride (Nb₃Cl₈) is a layered two-dimensional semiconducting material with many exotic properties including a breathing kagome lattice, a topological flat band in its band structure, and a crystal structure that undergoes a structural and magnetic phase transition at temperatures below 90 K. Despite being a remarkable material with fascinating new physics, the understanding of its phonon properties is at its infancy. In this study, we investigate the phonon dynamics of Nb₃Cl₈in bulk and few layer flakes using polarized Raman spectroscopy and density-functional theory (DFT) analysis to determine the material’s vibrational modes, as well as their symmetrical representations and atomic displacements. We experimentally resolved 12 phonon modes, five of which areA_1gmodes while the remaining seven areE_gmodes, which is in strong agreement with our DFT calculation. Layer-dependent results suggest that the Raman peak positions are mostly insensitive to changes in layer thickness, while peak intensity and full width at half maximum are affected. Raman measurements as a function of excitation wavelength (473–785 nm) show a significant increase of the peak intensities when using a 473 nm excitation source, suggesting a near resonant condition. Temperature-dependent Raman experiments carried out above and below the transition temperature did not show any change in the symmetries of the phonon modes, suggesting that the structural phase transition is likely from the high temperatureP $\overline{\text{3}m}$ 1 phase to the low-temperatureR $\overline{3m}$ phase. Magneto-Raman measurements carried out at 140 and 2 K between −2 and 2 T show that the Raman modes are not magnetically coupled. Overall, our study presented here significantly advances the fundamental understanding of layered Nb₃Cl₈material which can be further exploited for future applications. 

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3. Intrinsic Thermal Transport Properties of ZrB ₂ From Room Temperature to Melting Point

   https://doi.org/10.1002/rar2.70315  

   Lee, Yeojin; Xu, Qihao; Jang, Hyejin; Feng, Tianli (May 2026, Rare Metals)

   ABSTRACT Zirconium diboride (ZrB₂) is a promising material for extreme‐environment applications, yet its intrinsic high‐temperature thermophysical behavior remains uncertain: Experiments are highly sensitive to processing conditions, simulations omit key mechanisms, and both rarely reach ultrahigh temperatures. Here, we predict the thermal conductivity (κ), heat capacity, and thermal expansion of ZrB₂from 300 to 3500 K using first principles, explicitly incorporating phonon and electron transport, high‐order phonon scattering, and temperature‐dependent force constants. We estimate that the intrinsic room‐temperature polycrystallineκis ∼169 W m⁻¹ K⁻¹, exceeding the highest experimental value (∼141 W m⁻¹ K⁻¹) limited by microstructural defects, and decreases monotonically to 64.5 W m⁻¹ K⁻¹at 3500 K. Remarkably, this magnitude rivals that of the most refractory metal, tungsten, whereas ZrB₂'s density is three times lower, underscoring its potential for lightweight thermal management. Importantly, electrons dominate heat transport across the entire temperature range, carrying ∼61% ofκat 300 K and ∼91% at 3500 K, indicating that previous research focused solely on phonon engineering may have overlooked the governing role of electronic conduction. The Lorenz number varies non‐monotonically with temperature, deviating significantly from the Sommerfeld valueL₀, indicating that the common assumption of constantL₀may lead to inaccurate thermal–electrical correlations. Phonons dominate heat capacity, though electronic contributions become notable above 1300 K (≈6% at 3500 K). For phonon transport, heat is primarily carried by acoustic modes (≈89% at 300 K) and limited by three‐phonon and electron‐phonon scattering. Counter‐intuitively, four‐phonon scattering is negligible at room temperature, despite the large acoustic–optical gap, because broad optical bands preserve key three‐phonon channels, though the four‐phonon scattering becomes significant at highT. Interestingly, isotopic purification would raise phonon thermal conductivity by ∼23%, whereas temperature‐dependent force constants increase it by 28% at room temperature. Finally, compared with related systems, ZrB₂exhibits nearly twice the thermal conductivity of ZrC at room temperature, mainly because of its significantly higher electronic contribution while maintaining a higher phonon component despite its more complex structure. Althoughκfor ZrB₂decreases with temperature, whereas that of ZrC rises, ZrB₂remains superior across the entire temperature range. This work clarifies the intrinsic thermal transport physics of ZrB₂and highlights its exceptional potential for high‐temperature thermal‐management and aerospace applications. 

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4. Raman spectroscopy of phonon states in NbTe ₄ and TaTe ₄ quasi‐one‐dimensional van der Waals crystals

   https://doi.org/10.1002/jrs.6661  

   Nataj, Zahra Ebrahim; Kargar, Fariborz; Krylyuk, Sergiy; Debnath, Topojit; Taheri, Maedeh; Ghosh, Subhajit; Zhang, Huairuo; Davydov, Albert V; Lake, Roger K; Balandin, Alexander A (June 2024, Journal of Raman Spectroscopy)

   Abstract We report the results of polarization‐dependent Raman spectroscopy of phonon states in single‐crystalline quasi‐one‐dimensional NbTe₄and TaTe₄van der Waals materials. The measurements were conducted in the wide temperature range from 80 to 560 K. Our results show that although both materials have identical crystal structures and symmetries, there is a drastic difference in the intensity of their Raman spectra. While TaTe₄exhibits well‐defined peaks through the examined wavenumber and temperature ranges, NbTe₄reveals extremely weak Raman signatures. The measured spectral positions of the phonon peaks agree with the phonon band structure calculated using the density‐functional theory. We offer possible reasons for the intensity differences between the two van der Waals materials. Our results provide insights into the phonon properties of NbTe₄and TaTe₄van der Waals materials and indicate the potential of Raman spectroscopy for studying charge‐density‐wave quantum condensate phases. 

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5. Spontaneously formed phonon frequency combs in van der Waals solid CrGeTe3 and CrSiTe3

   https://doi.org/10.1038/s41467-025-61173-7  

   Chen, Lebing; Ye, Gaihua; Nnokwe, Cynthia; Pan, Xing-Chen; Tanigaki, Katsumi; Cheng, Guanghui; Chen, Yong P; Yan, Jiaqiang; Mandrus, David G; Llacsahuanga_Allcca, Andres E; et al (December 2025, Nature Communications)

   Abstract Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe₃(X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highestA_gmode in CrGeTe₃splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge₂Te₆clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe₃, demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies. 

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