Photoinduced charge transfer in van der Waals heterostructures occurs on the 100 fs timescale despite weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind this ultrafast process and the role of the lattice in mediating it. Here, using femtosecond electron diffraction, we directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following the selective excitation of WSe2, we measure the concurrent heating of both WSe2 and WS2 on a picosecond timescale—an observation that is not explained by phonon transport across the interface. Using first-principles calculations, we identify a fast channel involving an electronic state hybridized across the heterostructure, enabling phonon-assisted interlayer transfer of photoexcited electrons. Phonons are emitted in both layers on the femtosecond timescale via this channel, consistent with the simultaneous lattice heating observed experimentally. Taken together, our work indicates strong electron–phonon coupling via layer-hybridized electronic states—a novel route to control energy transport across atomic junctions.
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The codes and analysis scripts that support the findings of this study are available from the corresponding authors upon reasonable request.
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We gratefully acknowledge M. Kozina, S. Park, D. Luo and T. Mattox for experimental support, and M. Naik for insightful discussions. A.R. gratefully acknowledges support through the Early Career LDRD Program of Lawrence Berkeley National Laboratory under US Department of Energy (DOE) contract no. DE-AC02-05CH11231. Sample fabrication at the Molecular Foundry was supported by the US DOE Office of Basic Energy Sciences under contract no. DE-AC02-05CH11231. E.C.R. and F.W. also acknowledge support from the US DOE, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05CH11231 (van der Waals heterostructure program KCFW16). Research at SLAC was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. The UED experiments were performed at the SLAC MeV-UED which is operated as part of the Linac Coherent Light Source at the SLAC National Accelerator Laboratory, supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The computational work was supported by the Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM), which is funded by the DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05CH11231, as part of the Computational Materials Sciences Program. We acknowledge the use of computational resources at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the DOE Office of Science under the above contract, using NERSC awards BES-ERCAP-2651 for the electronic structure calculations and BES-ERCAP-m3606 for the molecular dynamics simulations. Additional computational resources were provided by the Extreme Science and Engineering Discovery Environment (XSEDE) supercomputer Stampede2 at the Texas Advanced Computing Center (TACC) through the allocation TG-DMR190070 for electron–phonon calculations. E.B. and J.D.G. acknowledgs support from the Natural Science and Engineering Research Council (NSERC) Canada through the Post-Graduate Scholarship PGS D3-502559-2017 and PGS D-568202-2022, respectively. E.C.R. acknowledges support from the Department of Defense through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. K.W. and T.T. acknowledge support from JSPS KAKENHI (grant nos. 19H05790, 20H00354 and 21H05233).
The authors declare no competing interests.
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Sood, A., Haber, J.B., Carlström, J. et al. Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer. Nat. Nanotechnol. 18, 29–35 (2023). https://doi.org/10.1038/s41565-022-01253-7