Structural Monoclinicity and Its Coupling to Layered Magnetism in Few-Layer CrI₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Few-layer chromium triiodide (CrI₃) exhibits unique magnetic and structural properties.
• Understanding its structural behavior under varying conditions is crucial for potential applications.

Purpose of the Study:

• To investigate the layer-number, temperature, and magnetic field dependence of Raman spectra in few-layer CrI₃.
• To elucidate the structural phase transitions and distortions in CrI₃.

Main Methods:

• Polarization-resolved Raman spectroscopy was employed.
• Measurements were conducted on one- to four-layer CrI₃ samples.
• Dependence on layer number, temperature, and magnetic field was analyzed.

Main Results:

• A doubly degenerated E_g mode in monolayer CrI₃ splits into A_g and B_g modes in thicker samples due to monoclinic stacking.
• The energy separation of these modes increases with thickness and shows temperature dependence, indicating a failed monoclinic-to-rhombohedral transition.
• An additional monoclinic distortion was observed during the antiferromagnetism-to-ferromagnetism phase transition induced by a magnetic field.

Conclusions:

• The observed spectral changes are attributed to a structural transformation involving lateral sliding and reduced interlayer distance.
• These findings provide insights into the complex structural dynamics of few-layer CrI₃.