Chiral Phonons and Anomalous Excitation-Energy-Dependent Raman Intensities in Layered AgCrP₂Se₆

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Layered two-dimensional materials exhibit structural anisotropy impacting optical absorption and phonon modes.
• Lattice orientation and excitation energy influence phonon mode intensities, enabling advanced phononic and optoelectronic devices.

Purpose of the Study:

• Investigate anomalous Raman spectra in single-crystalline AgCrP2Se6, a layered antiferromagnetic material.
• Characterize chiral phonon modes and their optical activities in bulk and exfoliated AgCrP2Se6.

Main Methods:

• Density functional theory (DFT) calculations.
• Experimental Raman spectroscopy measurements on bulk and exfoliated AgCrP2Se6 crystals.
• Analysis of excitation energy-dependent and temperature-dependent peak intensities.

Main Results:

• Observed anomalous Raman spectra in AgCrP2Se6, including three chiral phonon modes.
• Chiral phonon modes exhibit significant Raman optical activity (circular intensity differences) in bulk material, decreasing with thickness.
• Strong excitation-energy-dependent peak intensities and apparent cooling effects (up to 220 K) were recorded.
• Anomalies attributed to ABC layer stacking and constrained metal ion environment leading to charge transfer and modified electron-phonon coupling.

Conclusions:

• AgCrP2Se6 displays unique phononic and optical properties due to its specific crystal structure and electronic interactions.
• The observed anomalies, including chiral phonon modes and apparent cooling, position AgCrP2Se6 for novel optical and phononic applications.
• This study provides insights into structure-property relationships in layered materials for next-generation technologies.