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Valley-selective optical Stark effect in monolayer WS2.

Edbert J Sie1, James W McIver2, Yi-Hsien Lee3

  • 1Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Nature Materials
|December 16, 2014
PubMed
Summary
This summary is machine-generated.

Researchers have lifted valley degeneracy in two-dimensional transition metal dichalcogenides (TMDs) using circularly polarized light. This breakthrough enables selective tuning of exciton levels, advancing valleytronics and topological phase research.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Optics

Background:

  • Breaking space-time symmetries in 2D crystals significantly impacts electronic properties.
  • Monolayer transition metal dichalcogenides (TMDs) possess broken inversion symmetry, enabling valley-selective electron populations.
  • Lifting valley degeneracy is crucial for valleytronics and band engineering.

Purpose of the Study:

  • To demonstrate the first direct evidence of lifted valley degeneracy in monolayer TMDs.
  • To explore a novel method for controlling the valley degree of freedom.
  • To investigate potential applications in valleytronic devices and Floquet topological phases.

Main Methods:

  • Utilizing intense circularly polarized light to break time-reversal symmetry.
  • Applying the optical Stark effect to selectively tune exciton energy levels.
  • Experimental investigation on monolayer tungsten disulfide (WS2).

Main Results:

  • Direct evidence of lifted valley degeneracy achieved in monolayer WS2.
  • Selective tuning of exciton levels in each valley by up to 18 meV.
  • Demonstration of optical Stark effect for valley control.

Conclusions:

  • Intense circularly polarized light offers a new pathway to control valley degeneracy in 2D TMDs.
  • This method provides enhanced control over the valley degree of freedom.
  • Potential for realizing new Floquet topological phases in 2D materials.