Mansour M. Al-Makeen

The coupling between phonon and spin gives rise to intriguing phenomena, including phonon Hall effect, spin Seebeck effect, and charge density wave (CDW). Here, we investigate spin–phonon coupling and CDW transition in antiferromagnetic intercalated Fe0.25TaSe2 using Raman spectroscopy. Fe intercalation introduces a new phonon mode: the spin–phonon mode (SPM) with two components, SPM1 and SPM2, stemming from vibration of the intercalated Fe atoms. Below the Néel temperature of 130 K, the position ratio of SPM1 and SPM2 modes exhibits anomalous change, and the linewidth of SPM2 broadens suddenly, demonstrating spin–phonon coupling mediated by the antiferromagnetic ordering. The two-phonon mode observed in Fe0.25TaSe2 attenuates rapidly at 170 K, notably higher than the CDW transition temperature in TaSe2 (T = 100 K), indicating the Fe intercalation benefits the CDW transition. In addition, the twisting mode in Fe0.25TaSe2 is significantly enhanced compared to that in TaSe2 and exhibits an unusual redshift and significant broadening in linewidth with decreasing temperature, indicating the intercalated Fe plays a “bridging” role, which gradually weakens as the temperature decreases. These findings provide valuable insights into electron–phonon–spin coupling in low-dimensional magnetic materials.

Semi-metallic 1 T -TiTe ₂ drew considerable interest owing to its intriguing structural properties. The emergence of charge density wave (CDW) in the single-layer 1 T -TiTe ₂ rather than bulk suggests that electron-phonon ( e-ph) coupling may play an important role in inducing CDW or superconductivity. The investigation into lattice anharmonicity, which is strongly linked to e-ph coupling, is still lacking. Here, we employed temperature-dependent Raman spectroscopy to investigate the e-ph coupling and anharmonic phonon–phonon ( ph-ph) interactions for the phonon modes in exfoliated 1 T -TiTe ₂ thin flakes (∼12 nm). The E _g mode exhibits a Breit–Wigner–Fano lineshape with linear frequency redshift, while both the M and A _1g modes show Gaussian/Lorentzian lineshapes with nonlinear softening frequency redshifts. Both E _g and A _1g linewidths show anomalous broadening with increasing temperature due to the interplay between the e-ph coupling and anharmonic ph-ph interactions. In contrast, the M mode exhibits monotonic linewidth broadening with temperature due to anharmonic ph-ph interactions. The e-ph coupling constants were extracted to be λ e − ph E g = 0.95 ± 0.09 , λ e − ph M = 0.05 ± 0.006 , and λ e − ph A 1 g = 0.19 ± 0.0 2 . These findings provide a profound understanding of anharmonic ph-ph interactions, e-ph coupling, and their thermodynamic properties in 1 T -TiTe ₂ , which can enhance the comprehension of phonon dynamics in various quantum materials.

Two-dimensional (2D) layered materials have received much attention due to the unique properties stemming from their van der Waals (vdW) interactions, quantum confinement, and many-body interactions of quasi-particles, which drive their exotic optical and electronic properties, making them critical in many applications. Here, we review our past years’ findings, focusing on many-body interactions in 2D layered materials, including phonon anharmonicity, electron–phonon coupling (e-ph), exciton dynamics, and phonon anisotropy based on temperature (polarization)-dependent Raman spectroscopy and Photoluminescence (PL). Our review sheds light on the role of quasi-particles in tuning the material properties, which could help optimize 2D materials for future applications in electronic and optoelectronic devices.

Twisted isotropic-anisotropic van der Waals heterostructures provide a platform for controlling the electronic and phononic properties of 2D materials and inducing in-plane anisotropy in some isotropic materials. Herein, angle-resolved polarized Raman spectroscopy and photoluminescence spectroscopy are used to investigate the induced in-plane anisotropy of the quasiparticles in the twisted MoS2/CrOCl heterostructures. Both the phonons (Eg2 MoS2 and Ag1 MoS2 modes) and excitons (A and B excitons) in MoS2 represent a strong in-plane orientation dependence, and the maximum intensities are along the [100]CrOCl. The induced anisotropy ratios of phonons vary continuously in the range from 1.22 to 1.13 for the Eg2 MoS2 mode and 1.15 to 1.09 for the Ag1 MoS2 mode with changing twisted angles, which originate from the anisotropic carrier mobility induced by the localized charge distribution from the anisotropic CrOCl substrates, and are further tuned by the uniaxial local limit of charge carriers caused by 1D moiré pattern. Our findings provide a way to controllably regulate the induced in-plane optical anisotropy in heterostructures.