Birefringence-Directed Raman Selection Rules in 2D Black Phosphorus Crystals

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Raman scattering in low symmetry crystals is affected by birefringence-induced depolarization.
• Classical Raman selection rules require correction for anisotropic materials to account for birefringence.

Purpose of the Study:

• To theoretically and experimentally investigate birefringence-directed Raman selection rules in anisotropic black phosphorus (BP) crystals.
• To explore the simplified system of 2D anisotropic materials for studying these rules.

Main Methods:

• Developed a theoretical model incorporating birefringence to interpret Raman scattering.
• Conducted experimental polarized Raman scattering measurements on thin BP crystals.
• Examined different Raman modes, laser lines, and BP sample thicknesses.

Main Results:

• The theoretical model successfully explained the abnormal angle-dependent polarized Raman scattering of Ag modes in thin BP.
• Observed deviations from classical Raman selection rules were attributed to birefringence.
• Results were consistent across various Raman modes, laser wavelengths, and sample thicknesses.

Conclusions:

• Birefringence plays a crucial role in dictating Raman selection rules in anisotropic 2D materials like BP.
• The study validates the modified selection rules and highlights the utility of 2D materials for such investigations.