Interlayer excitons with polarizability reveal gradual-to-abrupt crossover in Mott transition

Optically generated Coulomb-bound electron–hole pairs in semiconductors – excitons – can dissociate at high excitation densities, resulting in an exciton Mott transition, a hallmark of quantum many-body phase transitions with broad relevance to optoelectronics. However, its nature has remained debated for decades, largely hindered by the difficulty to deliberately tune exciton-exciton interactions. Here we realize a four-layer 2D heterostructure hosting interlayer excitons with record-high polarizability and uncover a continuous evolution from gradual to abrupt Mott transitions. In this platform, an electric field drives excitonic wavefunction redistribution, enabling in situ control of the exciton dipole moment via a quadratic Stark response, thereby tuning exciton interactions at fixed density. This establishes the exciton dipole moment as a continuous control knob for bosonic quantum phase transitions, reconciling long-standing experimental discrepancies and opening routes to emergent excitonic quantum matter.