The phonon thermal Hall angle in black phosphorus

Area of Science:

• Condensed Matter Physics
• Materials Science
• Thermal Transport

Background:

• The origin of the phonon thermal Hall Effect (THE) in insulators remains largely unidentified.
• Previous observations of THE have shown significant variations in amplitude across different materials.

Purpose of the Study:

• To investigate the thermal Hall conductivity in black phosphorus, a non-magnetic elemental insulator.
• To understand the underlying mechanisms responsible for THE in insulating materials.

Main Methods:

• Experimental measurement of longitudinal and transverse thermal conductivities in black phosphorus under varying magnetic fields.
• Analysis of phonon behavior, including mode anti-crossing and phonon mean-free-path.

Main Results:

• Observed a thermal Hall conductivity in black phosphorus with an amplitude exceeding previously reported values.
• Found that longitudinal and transverse thermal conductivities peak at the same temperature.
• Demonstrated that the thermal Hall angle in black phosphorus is not correlated with the phonon mean-free-path.

Conclusions:

• The study presents a significant observation of THE in a non-magnetic elemental insulator, black phosphorus.
• Identified phonon mode anti-crossing as a key factor facilitating wave-like transport across modes.
• Proposed that anisotropic charge distribution around atomic bonds may mediate the coupling between phonons and magnetic fields, offering a new avenue for THE research.