Evidence for a spin acoustic surface plasmon from inelastic atom scattering

Area of Science:

• Surface Science
• Condensed Matter Physics
• Materials Science

Background:

• Closed-shell atoms interacting with metal surfaces involve energy and momentum exchange primarily through surface valence electrons, creating virtual electron-hole pairs.
• These electron-hole pairs can decay into surface phonons or acoustic surface plasmons (ASPs).
• Acoustic surface plasmons (ASPs) have not been previously observed using inelastic atom scattering (IAS).

Purpose of the Study:

• To provide evidence for the observation of acoustic surface plasmons (ASPs) in Ni(111) using inelastic atom scattering (IAS).
• To investigate the coupling of ASPs with phonons and their behavior within the surface-projected phonon continuum.
• To characterize the nature of ASPs in Ni(111) and identify them as a new type of quasiparticle.

Main Methods:

• Experimental observation of ASPs using Ne and He atom scattering on Ni(111).
• Theoretical analysis involving self-consistent calculations of the surface response function to atom collisions.
• First-principle calculations of the surface-phonon dynamics of Ni(111).

Main Results:

• Evidence for ASPs in Ni(111) was successfully obtained using both Ne and He atom scattering.
• He atom scattering revealed the coupling of ASPs with phonons, leading to reduced ASP velocity and potential avoided crossings with optical surface phonon branches.
• Calculations confirmed that ASPs in Ni(111) originate from the majority-spin Shockley surface state, identifying them as Spin Acoustic Surface Plasmons (SASPs).

Conclusions:

• The study presents the first experimental evidence of acoustic surface plasmons (ASPs) in Ni(111) via inelastic atom scattering.
• The findings demonstrate the coupling of ASPs with phonons and introduce Spin Acoustic Surface Plasmons (SASPs) as a novel collective quasiparticle.
• This research expands the understanding of surface dynamics and electron-phonon interactions in metals.