Spin-patterned plasmonics: towards optical access to topological-insulator surface states

Area of Science:

• Condensed Matter Physics
• Plasmonics
• Spintronics

Background:

• Topological insulators (TI) exhibit unique surface states (SS) with spin-momentum locking, crucial for spintronics.
• Efficiently coupling light to these nanoscale SS is challenging due to bulk light interactions.
• Optical angular momentum coupling to TI SS is of fundamental and applied interest.

Purpose of the Study:

• To propose and demonstrate a plasmonic cavity for nanoscale light confinement.
• To control the spin angular momentum (AM) of surface plasmon-polaritons (SPPs).
• To enable coupling of optical AM to topological insulator surface states.

Main Methods:

• Theoretical proposal of a plasmonic cavity design.
• Experimental demonstration using near-field measurements.
• Fabrication of a gold-air interface plasmonic structure.

Main Results:

• Demonstrated nanoscale light confinement and SPP AM control.
• Observed a "chess-board-like" pattern of SPP field components.
• Each pattern element showed uniform circular polarization (spin AM) and out-of-plane field vortices (orbital AM).
• Experimental results showed excellent agreement with theoretical predictions.

Conclusions:

• The plasmonic cavity effectively controls SPP AM for light-matter interaction.
• This approach offers a pathway for efficient optical access to topological insulator surface states.
• The findings support the development of advanced spintronic devices.