Polaronic electron crystals and nano-acoustics in van der Waals heterostructures

Realizing quantum phases of electrons with high critical temperatures (Tc) has been one of the most important goals in quantum materials research. Recently, two-dimensional moiré materials have emerged as the most versatile platforms for realizing quantum phases. The correlated Mott insulator states in transition metal dichalcogenide (TMD) moiré interfaces exhibit sufficiently high Tc, e.g., ~ 150 K. Here, we explore the stability origins of these correlated states in WSe₂/WS₂ moiré superlattices. We find that ultrafast electronic excitation leads to melting of the Mott states on time scales five times longer than predictions from the charge hopping integrals and the melting rates are thermally activated, which matches well with DFT calculation of polaron formation. These findings reveal a close interplay of electron-electron and electron-phonon interactions in stabilizing the polaronic Mott insulators at TMD moiré interfaces. Along with understanding the dynamics of melting and recrystallization of electron crystals, we also demonstrate a way to launch and temporally control the acoustic waves in vdW heterostructures. The precise control of phonon coherence, dynamics, and propagation gives us access to the tunability of all material properties that are dependent on the phonon physics and possibly realize phononic devices for communication and information technologies in the future.