Harmonic to anharmonic tuning of moiré potential leading to unconventional Stark effect and giant dipolar repulsion in WS2/WSe2 heterobilayer

Suman Chatterjee; Medha Dandu; Pushkar Dasika; Rabindra Biswas; Sarthak Das; Kenji Watanabe; Takashi Taniguchi; Varun Raghunathan; Kausik Majumdar

doi:10.1038/s41467-023-40329-3

Journal article Harmonic to anharmonic tuning of moiré potential leading to unconventional Stark effect and giant dipolar repulsion in WS2/WSe2 heterobilayer

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Suman Chatterjee, Medha Dandu, Pushkar Dasika, Rabindra Biswas, Sarthak Das, Kenji Watanabe, Takashi Taniguchi, Varun Raghunathan, Kausik Majumdar. Harmonic to anharmonic tuning of moiré potential leading to unconventional Stark effect and giant dipolar repulsion in WS2/WSe2 heterobilayer. Nature Communications. 2023, 14 (1), 4679. https://doi.org/10.1038/s41467-023-40329-3

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Excitonic states trapped in harmonic moir ́e wells in twisted heterobilayers is an excellent platform to study many-body interaction. However, the moir ́e exciton potential is primarily governed by the rigid twist angle, and its dynamic tuning thus remains a challenge - a knob which would be highly desirable for both scientific exploration and device applications. Using moir ́e trapped excitonic emission as a probe, here we demonstrate dynamic tuning of moir ́e potential in a WS2/WSe2 heterobilayer through two anharmonic perturbations, induced by gate voltage and optical power. First, we show that, dictated by the Poisson equation, a gate voltage can result in a local in-plane perturbing field with odd parity around the high-symmetry points. This allows us to simultaneously observe the first (linear) and second (parabolic) order Stark shift for the ground state and first excited state, respectively, of the moir ́e trapped exciton - an effect exactly opposite to conventional quantum-confined Stark shift. Depending on the degree of confinement, the moir ́e trapped excitons exhibit up to twenty-fold gate-tunability in the lifetime (100 ns to 5 ns). The second anharmonic tuning is demonstrated through exciton localization dependent dipolar repulsion, leading to an optical power-induced blueshift as high as ∼1 meV/μW, which is about 5 times higher than previous reports.

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