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

Excitonic states trapped in harmonic moire wells of twisted heterobilayers is an intriguing testbed for exploring many-body physics. However, the moire potential is primarily governed by the twist angle, and its dynamic tuning remains a challenge. Here we demonstrate anharmonic tuning of moire potential in a WS2/WSe2 heterobilayer through gate voltage and optical power. 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 moire trapped exciton - an effect opposite to conventional quantum-confined Stark shift. Depending on the degree of confinement, these excitons exhibit up to twenty-fold gate-tunability in the lifetime (100 to 5 ns). Also, exciton localization dependent dipolar repulsion leads to an optical power-induced blueshift of similar to 1 meV/mu W - a five-fold enhancement over previous reports.