Quantum Phase Transitions of Interlayer Excitons in van der Waals Heterostructures

Quantum phases of interlayer excitons (IXs) in van der Waals heterostructures (vdWHs) play a critical role in determining the fundamental properties of these structures. However, quantum phase transitions between free state and self‐trapped state of IXs remain poorly understood. Herein, the physical pictures for quantum transitions of IXs stemming from the IX–interface optical phonon coupling are explored. The critical boundaries of the phase transitions among free, light, and heavy self‐trapped states are given and the dependence of boundaries on the structural parameters of vdWHs is discussed, implying the controllability of these IXs states in vdWHs. In order to distinguish different quantum phases further, a strategy that multiphonon Raman scattering mediated by these exciton states is proposed. It is found find that multiphonon overtones appear in Raman spectra for the self‐trapped states and not for free states, which clarifies the long‐standing puzzle that free exciton can induce multiphonon Raman processes. The results lay the significant theoretical foundation for understanding the quantum phases of IX and their modulation in vdWHs.