Coherent acoustic phonons in a coupled hexagonal boron nitride-graphite heterostructure

Area of Science:

• Condensed Matter Physics
• Materials Science
• Ultrafast Spectroscopy

Background:

• Van der Waals heterostructures, like graphite/hBN, are promising for advanced electronic devices.
• Understanding carrier dynamics and heat transfer in these materials is critical for device performance and stability.

Purpose of the Study:

• To investigate coherent acoustic phonon modes (CAPs) in a free-standing graphite/hBN heterostructure.
• To elucidate the excitation mechanisms and strain dynamics of CAPs.
• To determine the heat transfer dynamics between graphite and hBN layers.

Main Methods:

• Femtosecond optical excitation of the graphite layer.
• Ultrafast electron diffraction for independent strain dynamics evaluation.
• Analytical and numerical linear-chain modeling for mode analysis.

Main Results:

• Three distinct CAP modes were identified in the bilayer system.
• The excitation mechanisms were inferred from the relative phases of the observed modes.
• Evidence for ultrafast heat transfer from graphite to the hBN lattice was found.

Conclusions:

• The study demonstrates the presence and characteristics of CAPs in graphite/hBN heterostructures.
• Ultrafast heat transfer is a significant mechanism in this material combination.
• These findings are essential for the design and optimization of devices utilizing graphite/hBN.