Spatially Coherent Tip-Enhanced Raman Spectroscopy Measurements of Electron-Phonon Interaction in a Graphene Device

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Raman scattering is a key technique for probing electron-phonon interactions in materials.
• Graphene's electronic properties are highly tunable via Fermi energy, influencing its optical and transport characteristics.
• Understanding coherence length is crucial for characterizing charge carrier behavior.

Purpose of the Study:

• To investigate the coherence length (Lc) of the Raman scattering process in graphene.
• To determine the dependence of Lc on Fermi energy.
• To explore the underlying physical mechanisms, such as Kohn anomaly and electron-phonon interactions.

Main Methods:

• Utilizing spatially coherent tip-enhanced Raman spectroscopy (TERS).
• Measuring the coherence length (Lc) as a function of Fermi energy.
• Analyzing the relationship between Lc, Fermi energy, and electron-phonon coupling.

Main Results:

• Coherence length (Lc) was observed to decrease as the Fermi energy approached the neutrality point.
• This decrease is consistent with the Kohn anomaly phenomenon in a ballistic transport regime.
• The results suggest significant variations in longitudinal optical phonon group velocity or electron energy uncertainty.

Conclusions:

• The study provides insights into electron-phonon interactions and transport properties in graphene.
• The observed phenomena highlight the importance of electron energy uncertainty and phonon group velocity.
• Spatially coherent TERS is a powerful tool for probing subtle electronic and phononic properties in 2D materials.