Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• The Rashba effect, a spin-orbit interaction, leads to spin splitting in electronic bands.
• Monolayer materials offer unique electronic properties due to quantum confinement.
• Circular Photogalvanic Effect (CPGE) is a mechanism to generate spin-polarized currents.

Purpose of the Study:

• To investigate the generation of nonreciprocal spin-polarized photocurrent in Tl-Pb monolayer alloys.
• To explore the role of the giant Rashba effect in Tl-Pb/Si(111) surface superstructures.
• To understand the CPGE mechanism in atomically thin materials.

Main Methods:

• Fabrication of Tl-Pb monolayer alloys on a Si(111) substrate.
• Illumination with obliquely shining circularly polarized near-infrared (IR) light.
• Measurement of spin-polarized photocurrent and analysis using a model for relative permittivity.

Main Results:

• Observed nonreciprocal spin-polarized photocurrent via CPGE exclusively in Tl-Pb alloy layers, not in single-element Tl or Pb layers.
• The magnitude of CPGE in these monolayer alloys is comparable to or larger than in many other spin-split thin-film materials.
• Model analysis indicated a relative permittivity (ε*) of approximately 1.0 for the monolayer alloys.

Conclusions:

• Tl-Pb monolayer alloys on Si(111) exhibit a giant Rashba effect enabling efficient CPGE.
• The unique electronic environment of the monolayer at the vacuum-substrate interface contributes to its properties.
• This study demonstrates the potential for optical manipulation of electron spins in monolayer materials.