Electrical Tuning of Optical Stark Effect in Monolayer WS2

Upon excitation by a strong coherent light field, photon-dressed states form and hybridize with equilibrium states, leading to transient band renormalization, a phenomenon known as the optical Stark effect (OSE). It offers a compelling approach to engineer the electronic structure, valley degeneracy and non-equilibrium topological properties on ultrafast timescales. Extensive research has been conducted on the optical control of the OSE by modulating the optical pump fluence, detuning energy and polarization. Herein, we present the electrical tuning of valley-selective OSE in a back-gated monolayer WS ₂ device using helicity-resolved transient absorption spectroscopy (TAS). Our results reveal a linear relationship between the OSE-induced blue shift and gate voltage with a slope of -0.07 meV/V. The mechanism involves the enhanced transition dipole moment as the device approaches charge neutrality through the photoinjected hole density. In addition, the exciton oscillator strength is found to scale linearly with the OSE-induced blue shift, under the conditions of fixed pump fluence and photon energy. Our study demonstrates the electrical tuning as an additional degree of freedom for Floquet engineering, and offering profound insights into coherent light-matter interaction in 2D materials.