Specular scattering probability of acoustic phonons in atomically flat interfaces

Area of Science:

• Condensed Matter Physics
• Materials Science
• Acoustics

Background:

• The Kapitza anomaly, a significant thermal boundary resistance, is observed at 1-10 K.
• Understanding acoustic phonon scattering at interfaces is crucial for thermal management in nanomaterials.
• Previous studies relied on indirect methods to infer interface properties.

Purpose of the Study:

• To directly determine the specular scattering probability of acoustic phonons at a crystal boundary.
• To investigate the role of atomic-scale corrugations in the Kapitza anomaly.
• To establish a method for non-destructively estimating subnanoscale roughness of buried interfaces.

Main Methods:

• Observation of coherent phonon escape from the coherent state during reflection.
• Utilizing sub-terahertz (sub-THz) frequency range where phonon wavelength exceeds lattice constant.
• Direct measurement of specular scattering probability at crystal boundaries.

Main Results:

• A direct determination of acoustic phonon specular scattering probability at crystal boundaries was achieved.
• Acoustic phonon-interface interaction in the sub-THz range aligns with macroscopic wave scattering theory for rough surfaces.
• The study quantitatively verifies that atomic-scale corrugations dominate the Kapitza anomaly.

Conclusions:

• Atomic-scale interface roughness is the primary cause of the Kapitza anomaly at low temperatures.
• The developed method provides a novel pathway for non-destructive estimation of subnanoscale buried interface roughness.
• This work bridges the gap between microscopic interface properties and macroscopic thermal transport phenomena.