Topologically Localized Vibronic Excitations in Second-Layer Graphene Nanoribbons

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Characterizing intrinsic properties of on-surface synthesized graphene nanoribbons (GNRs), such as topological end states, is crucial.
• Strong electronic interactions with metal substrates often obscure the unique features of GNRs.

Purpose of the Study:

• To investigate vibronic excitations of topological end states in self-decoupled second-layer GNRs.
• To understand the interplay between electronic, vibrational, and topological properties in GNRs.

Main Methods:

• Developed an on-surface squeezing-induced spillover strategy for growing self-decoupled second-layer GNRs.
• Utilized experimental techniques to study vibronic excitations.
• Performed theoretical calculations for mode assignment and analysis.

Main Results:

• Observed highly spatially localized vibronic progressions at the ends of second-layer GNRs.
• Attributed the localization to the extended lifetime of charging via resonant electron tunneling at topological end states.
• Assigned specific vibrational modes mediating the excitations and identified spatial distribution characteristics beyond the Franck-Condon picture.

Conclusions:

• The direct growth of second-layer GNRs offers an effective method to study their intrinsic properties.
• The findings provide insights into the coupling of electronic, vibrational, and topological characteristics in GNRs.
• The observed vibronic excitations offer a new avenue for probing topological states in low-dimensional materials.