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Direct coupling of light to valley current.

S Sharma1,2, D Gill3, J Krishna3

  • 1Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, 12489, Berlin, Germany. geet1729@gmail.com.

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Circularly polarized light can now control valley currents in 2D materials. Ultrafast light pulses create a momentum space valley dipole, enabling direct manipulation of valley charge and current for novel valleytronic devices.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Electronics

Background:

  • Two-dimensional (2D) semiconductors offer unique electronic properties based on the valley degree of freedom.
  • Current methods using circularly polarized light primarily couple to valley charge, not valley current, limiting valleytronic device control.
  • Lightwave manipulation of valley current is crucial for advanced valleytronic applications.

Purpose of the Study:

  • To demonstrate direct lightwave control of valley current in 2D materials.
  • To explore the underlying physical mechanism enabling valley current manipulation.
  • To investigate the potential for ultrafast valleytronic devices.

Main Methods:

  • Theoretical modeling using minimal tight-binding models for transition metal dichalcogenides and biased bilayer graphene.
  • Simulations employing time-dependent density functional theory (TD-DFT) with transient excitonic effects.
  • Analysis of the emergent vectorial character of few-cycle circularly polarized light pulses.

Main Results:

  • Few-cycle circularly polarized light directly couples to valley current, contradicting previous understanding.
  • An emergent momentum space valley dipole is identified as the key physical mechanism.
  • Complete control over valley current direction and magnitude is achieved via the valley dipole.
  • Valley currents are generated on femtosecond timescales (1-14 fs), potentially overcoming quantum decoherence.

Conclusions:

  • Ultrafast light-matter interactions can unlock new degrees of freedom in 2D materials.
  • The direct manipulation of valley current opens avenues for novel valleytronic devices.
  • Emergent phenomena in the ultrafast regime offer exciting possibilities for quantum electronics.