The coupling between electronic and lattice (vibrational) degrees of freedom plays a critical role in the carrier dynamics, interfacial thermal transport, and the emergence of strongly correlated phases in quantum materials. Using ultrafast electron diffraction (UED) spectroscopy, we investigated photoinduced non-equilibrium phonon dynamics in twisted MoS2/WS2 and WSe2/MoSe2 heterobilayers, uncovering an interlayer heat transfer channel with ~ 20 ps timescale – an order of magnitude faster than predicted by molecular dynamics simulations. This rapid transfer is driven by nonthermal phonon populations arising from electron-phonon scattering upon interlayer charge transfer. These findings are further validated by ultrafast diffuse scattering, which directly uncovers the momentum-resolved phonon distributions. Beyond flat nanostructures, we have developed monolayer-based 0D and 1D nano bubble-wrap structures with periodicity comparable with phonon mean free path, demonstrating promising potential for nanoscale thermal management. In small angle twisted WSe2/MoSe2, we demonstrated that photoexcitation drives coherent twisting and untwisting of the superlattice domains with sub-THz frequency. Going forward, we aim to harness and control these complex vibronic couplings to achieve ultrafast manipulation of quantum phenomena across multiple levels of spatial confinements.
Selected Publications
· Johnson, A. C., Georgaras, J. D., Shen, X., Yao, H., Saunders, A. P., Zeng, H. J., Kim, H., Sood, A., Heinz, T. F., Lindenberg, A. M., Luo, D., Jornada, F. H., and Liu, F. Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures. Science Adv. 10(4), eadj8819 (2024).
· Liu, F. Time- and angle-resolved photoemission spectroscopy (tr-arpes) of tmdc monolayers and bilayers. Chem. Sci. 14, 736–750 (2023).
· Kobayashi, Y., Heide, C., Johnson, A. C., Tiwari, V., Liu, F., Reis, D. A., Heinz, T. F., and Ghimire, S. Floquet engineering of strongly driven excitons in monolayer tungsten disulfide. Nat. Phys. 19(2), 171–176 (2023).
· Heide, C., Kobayashi, Y., Johnson, A. C., Liu, F., Heinz, T. F., Reis, D. A., and Ghimire, S. “probing electron-hole coherence in strongly driven 2d materials using high-harmonic generation”. Optica 9(5), 512–516 (2022).
