Phonon-coupled ultrafast interlayer charge oscillation at van der Waals heterostructure interfaces

Van der Waals (vdW) heterostructures of transition-metal dichalcogenide (TMD) semiconductors are central not only for fundamental science, but also for electro- and optical-device technologies where the interfacial charge transfer is a key factor. Ultrafast interfacial charge dynamics has been intensively studied, however, the atomic scale insights into the effects of the electron-phonon (e-p) coupling are still lacking. In this paper, using time dependent ab initio nonadiabatic molecular dynamics, we study the ultrafast interfacial charge transfer dynamics of two different TMD heterostructures ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$ and ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$, which have similar band structures but different phonon frequencies. We found that ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$ has softer phonon modes compared to ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$, and thus phonon-coupled charge oscillation can be excited with sufficient phonon excitations at room temperature. In contrast, for ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$, phonon-coupled interlayer charge oscillations are not easily excitable. Our study provides an atomic level understanding on how the phonon excitation and e-p coupling affect the interlayer charge transfer dynamics, which is valuable for both the fundamental understanding of ultrafast dynamics at vdW hetero-interfaces and the design of novel quasi-two-dimensional devices for optoelectronic and photovoltaic applications.