Abstract
Breaking the valley degeneracy in monolayer transition metal dichalcogenides through the valley-selective optical Stark effect (OSE) can be exploited for classical and quantum valleytronic operations such as coherent manipulation of valley superposition states. The strong light-matter interactions responsible for the OSE have historically been described by a two-level dressed-atom model, which assumes noninteracting particles. Here we experimentally show that this model, which works well in semiconductors far from resonance, does not apply for excitation near the exciton resonance in monolayer WS2. Instead, we show that an excitonic model of the OSE, which includes many-body Coulomb interactions, is required. We confirm the prediction from this theory that many-body effects between virtual excitons produce a dominant blue-shift for photoexcitation detuned from resonance by less than the exciton binding energy. As such, we suggest that our findings are general to low-dimensional semiconductors that support bound excitons and other many-body Coulomb interactions.
Highlights
Breaking the valley degeneracy in monolayer transition metal dichalcogenides through the valley-selective optical Stark effect (OSE) can be exploited for classical and quantum valleytronic operations such as coherent manipulation of valley superposition states
To exploit the chiral optical selection rules in WS21, shown in Fig. 1b, we use both a circularly polarized pump excitation pulse to drive dynamics in a particular valley as well as a circularly polarized white-light probe pulse to observe the changes induced in either valley
We can observe reduced absorption associated with state filling[28], photo-induced absorption associated with excited state transitions, changes in absorption line width, and spectral shifts in energy levels associated with the OSE4, dynamic Coulomb screening[31,36], and lattice heating[37]
Summary
Breaking the valley degeneracy in monolayer transition metal dichalcogenides through the valley-selective optical Stark effect (OSE) can be exploited for classical and quantum valleytronic operations such as coherent manipulation of valley superposition states. The coherent interaction of the ground and excited states with the light field gives rise to so-called Floquet states These are hybrid light−matter states consisting of the electronic energy levels, e.g. ground and exciton states |g〉 and |x〉 respectively, dressed by a photon, e.g. to form |g ± hυ〉 and |x ± hυ〉 respectively. The underlying physics of this process is similar to the formation of molecular excitons[20] and is analogous to avoided crossing behavior between light and matter states through strong coupling in photonic cavities[21] Though this picture treats the excited states as noninteracting particles, it has been applied to low-dimensional semiconductors where reduced electrostatic screening produces strong many-body interactions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
