Combining THz and Infrared Light to Control Valley Charge and Current in Gapless Graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Electronics

Background:

• Graphene's potential in valleytronics is limited by the lack of a selection rule for light-based valley coupling.
• Existing methods struggle to achieve efficient valley polarization and current control in graphene.

Purpose of the Study:

• To overcome the limitations in graphene valleytronics by developing a novel light-based control mechanism.
• To demonstrate precise control over valley charge and valley current in graphene using tailored light pulses.

Main Methods:

• Utilizing a combination of linearly polarized terahertz (THz) light and circularly polarized infrared light.
• Employing *ab initio* simulations to investigate the underlying physical mechanisms.
• Analyzing the momentum space dynamics and charge de-excitation processes.

Main Results:

• Achieved near-perfect valley charge polarization and complete light control over valley current.
• Identified a THz-induced momentum space shift mechanism responsible for charge generation and polarization.
• Observed ultrafast de-excitation leading to highly efficient valley polarization.

Conclusions:

• The proposed dual-polarization light scheme effectively addresses the selection rule limitations in graphene valleytronics.
• This approach offers a pathway for controlling valley dynamics in various gapless materials, including Xenes and few-layer graphene.
• Paves the way for practical applications of graphene and related materials in valleytronic devices.