Slow and highly confined plasmons observed in atomically thin TaS₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanophotonics

Background:

• Ultrathin transition metal dichalcogenides (TMDs), particularly tantalum-based materials, are theoretically predicted to support extreme light confinement.
• Achieving atomic-scale light confinement is crucial for developing next-generation optical and electronic devices.

Purpose of the Study:

• To experimentally observe and characterize highly confined plasmons in 2H-tantalum disulfide (TaS2) monolayers and bilayers.
• To investigate the momentum dispersion and confinement properties of these plasmons.

Main Methods:

• Momentum-resolved electron energy loss spectroscopy (q-EELS) with high momentum resolution (0.0056 Å⁻¹).
• Analysis of 2D plasmon resonances and their behavior at large wave vectors (q = 0.15 Å⁻¹).

Main Results:

• Observation of momentum-dispersed 2D plasmon resonances in 2H-TaS2 monolayers and bilayers.
• Achieved a lateral confinement ratio of up to 300, indicating significant light localization.
• Observed slow light behavior with a group velocity of approximately 10⁻⁴c.
• Identified a transition from 2D to 3D Coulomb interaction, corresponding to light confinement volumes of 1-2 nm³.
• Found that resonant modes do not enter the electron-hole continuum.

Conclusions:

• Experimental validation of extreme light confinement in ultrathin 2H-TaS2.
• Demonstrated potential for enhanced optical field confinement at cryogenic temperatures due to non-entry into the electron-hole continuum.
• Highlights 2H-TaS2 as a promising material for future nanophotonic applications requiring atomic-scale light manipulation.