Large, valley-exclusive Bloch-Siegert shift in monolayer WS2

Abstract

Coherent light-matter interaction can be used to manipulate the energy levels of atoms, molecules and solids. When light with frequency ω is detuned away from a resonance ωo, repulsion between the photon-dressed (Floquet) states can lead to a shift of energy resonance. The dominant effect is the optical Stark shift (1/(ω0-ω)), but there is an additional contribution from the so-called Bloch-Siegert shift (1/(ωo+ω)). Although it is common in atoms and molecules, the observation of Bloch-Siegert shift in solids has so far been limited only to artificial atoms since the shifts were small (<1 μeV) and inseparable from the optical Stark shift. Here we observe an exceptionally large Bloch-Siegert shift (~10 meV) in monolayer WS2 under infrared optical driving by virtue of the strong light-matter interaction in this system. Moreover, we can disentangle the Bloch-Siegert shift entirely from the optical Stark shift, because the two effects are found to obey opposite selection rules at different valleys. By controlling the light helicity, we can confine the Bloch-Siegert shift to occur only at one valley, and the optical Stark shift at the other valley. Such a valley-exclusive Bloch-Siegert shift allows for enhanced control over the valleytronic properties in two-dimensional materials, and offers a new avenue to explore quantum optics in solids.

References in corpus (7)

• Valley polarization in MoS2 monolayers by optical pumping
• Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition
• The Valley Hall Effect in MoS2 Transistors
• Beyond the Jaynes-Cummings model: circuit QED in the ultrastrong coupling regime
• Strong light-matter coupling in two-dimensional atomic crystals
• Observation of the Bloch-Siegert Shift in a Qubit-Oscillator System in the Ultrastrong Coupling Regime
• Ultrafast Generation of Pseudo-magnetic Field for Valley Excitons in WSe2 Monolayers

Cited by in corpus (7)

• Engineering symmetry breaking in two-dimensional layered materials
• Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers
• Exciton-Scattering-Induced Dephasing in Two-Dimensional Semiconductors
• Valley-selective optical Stark effect probed by Kerr rotation
• Floquet engineering of twisted double bilayer graphene
• Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides
• Quantum interference between the optical Stark effect and resonant harmonic generation in WS2