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# Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer

## Abstract

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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## Data availability

The data underlying Figs. 14 and Supplementary Figs. 317 are available via Zenodo at https://doi.org/10.5281/zenodo.7328935.

## Code availability

The codes and analysis scripts that support the findings of this study are available from the corresponding authors upon reasonable request.

## References

1. Geim, A. K. & Grigorieva, I. V. Van der Waals heterostructures. Nature 499, 419–425 (2013).

2. Lee, C.-H. et al. Atomically thin p–n junctions with van der Waals heterointerfaces. Nat. Nanotechnol. 9, 676–681 (2014).

3. Paul, K. K., Kim, J.-H. & Lee, Y. H. Hot carrier photovoltaics in van der Waals heterostructures. Nat. Rev. Phys. 3, 178–192 (2021).

4. Hong, X. et al. Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures. Nat. Nanotechnol. 9, 682–686 (2014).

5. Zhu, H. et al. Interfacial charge transfer circumventing momentum mismatch at two-dimensional van der Waals heterojunctions. Nano Lett. 17, 3591–3598 (2017).

6. Jin, C. et al. Ultrafast dynamics in van der Waals heterostructures. Nat. Nanotechnol. 13, 994–1003 (2018).

7. Kim, S. E. et al. Extremely anisotropic van der Waals thermal conductors. Nature 597, 660–665 (2021).

8. Vaziri, S. et al. Ultrahigh thermal isolation across heterogeneously layered two-dimensional materials. Sci. Adv. 5, eaax1325 (2019).

9. Sood, A. et al. Engineering thermal transport across layered graphene–MoS2 superlattices. ACS Nano 15, 19503–19512 (2021).

10. Li, X. et al. Intrinsic electrical transport properties of monolayer silicene and MoS2 from first principles. Phys. Rev. B 87, 115418 (2013).

11. Ma, E. Y. et al. Recording interfacial currents on the subnanometer length and femtosecond time scale by terahertz emission. Sci. Adv. 5, eaau0073 (2019).

12. Yuan, L. et al. Photocarrier generation from interlayer charge-transfer transitions in WS2-graphene heterostructures. Sci. Adv. 4, e1700324 (2018).

13. Luo, D. et al. Twist-angle-dependent ultrafast charge transfer in MoS2-graphene van der Waals heterostructures. Nano Lett. 21, 8051–8057 (2021).

14. Mannebach, E. M. et al. Dynamic structural response and deformations of monolayer MoS2 visualized by femtosecond electron diffraction. Nano Lett. 15, 6889–6895 (2015).

15. Weathersby, S. P. et al. Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory. Rev. Sci. Instrum. 86, 073702 (2015).

16. Shen, X. et al. Femtosecond mega-electron-volt electron microdiffraction. Ultramicroscopy 184, 172–176 (2018).

17. Sokolowski-Tinten, K. et al. Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction. Struct. Dyn. 4, 054501 (2017).

18. Kang, J., Tongay, S., Zhou, J., Li, J. & Wu, J. Band offsets and heterostructures of two-dimensional semiconductors. Appl. Phys. Lett. 102, 012111 (2013).

19. Zhou, H., Zhao, Y. & Zhu, H. Dielectric environment-robust ultrafast charge transfer between two atomic layers. J. Phys. Chem. Lett. 10, 150–155 (2019).

20. Rigosi, A. F., Hill, H. M., Li, Y., Chernikov, A. & Heinz, T. F. Probing interlayer interactions in transition metal dichalcogenide heterostructures by optical spectroscopy: MoS2/WS2 and MoSe2/WSe2. Nano Lett. 15, 5033–5038 (2015).

21. Yalon, E. et al. Energy dissipation in monolayer MoS2 electronics. Nano Lett. 17, 3429–3433 (2017).

22. Baroni, S., de Gironcoli, S., Dal Corso, A. & Giannozzi, P. Phonons and related crystal properties from density-functional perturbation theory. Rev. Mod. Phys. 73, 515–562 (2001).

23. Wang, Y., Wang, Z., Yao, W., Liu, G.-B. & Yu, H. Interlayer coupling in commensurate and incommensurate bilayer structures of transition-metal dichalcogenides. Phys. Rev. B 95, 115429 (2017).

24. Ji, Z. et al. Robust stacking-independent ultrafast charge transfer in MoS2/WS2 bilayers. ACS Nano 11, 12020–12026 (2017).

25. Wang, K. et al. Interlayer coupling in twisted WSe2/WS2 bilayer heterostructures revealed by optical spectroscopy. ACS Nano 10, 6612–6622 (2016).

26. Liu, F., Li, Q. & Zhu, X.-Y. Direct determination of momentum-resolved electron transfer in the photoexcited van der Waals heterobilayer WS2/MoS2. Phys. Rev. B 101, 201405 (2020).

27. Zheng, Q. et al. Phonon-assisted ultrafast charge transfer at van der Waals heterostructure interface. Nano Lett. 17, 6435–6442 (2017).

28. Tian, Y., Zheng, Q. & Zhao, J. Tensile strain-controlled photogenerated carrier dynamics at the van der Waals heterostructure interface. J. Phys. Chem. Lett. 11, 586–590 (2020).

29. Wang, Z. et al. Phonon-mediated interlayer charge separation and recombination in a MoSe2/WSe2 heterostructure. Nano Lett. 21, 2165–2173 (2021).

30. Lin, M.-F. et al. Ultrafast non-radiative dynamics of atomically thin MoSe2. Nat. Commun. 8, 1745 (2017).

31. Poellmann, C. et al. Resonant internal quantum transitions and femtosecond radiative decay of excitons in monolayer WSe2. Nat. Mater. 14, 889–893 (2015).

32. Lien, D.-H. et al. Electrical suppression of all nonradiative recombination pathways in monolayer semiconductors. Science 364, 468–471 (2019).

33. Kim, H., Uddin, S. Z., Higashitarumizu, N., Rabani, E. & Javey, A. Inhibited nonradiative decay at all exciton densities in monolayer semiconductors. Science 373, 448–452 (2021).

34. Merkl, P. et al. Twist-tailoring Coulomb correlations in van der Waals homobilayers. Nat. Commun. 11, 2167 (2020).

35. van der Zande, A. M. et al. Tailoring the electronic structure in bilayer molybdenum disulfide via interlayer twist. Nano Lett. 14, 3869–3875 (2014).

36. Bradley, A. J. et al. Probing the role of interlayer coupling and Coulomb interactions on electronic structure in few-layer MoSe2 nanostructures. Nano Lett. 15, 2594–2599 (2015).

37. Majumdar, A. & Reddy, P. Role of electron–phonon coupling in thermal conductance of metal–nonmetal interfaces. Appl. Phys. Lett. 84, 4768–4770 (2004).

38. Tomko, J. A. et al. Long-lived modulation of plasmonic absorption by ballistic thermal injection. Nat. Nanotechnol. 16, 47–51 (2021).

39. Li, Y. et al. Measurement of the optical dielectric function of monolayer transition-metal dichalcogenides: MoS2, MoSe2, WS2, and WSe2. Phys. Rev. B 90, 205422 (2014).

40. Byrnes, S. J. Multilayer optical calculations. Preprint at https://arxiv.org/abs/1603.02720 (2016).

41. Giannozzi, P. et al. Advanced capabilities for materials modelling with Quantum ESPRESSO. J. Phys. Condens. Matter 29, 465901 (2017).

42. Steinhoff, A. et al. Exciton fission in monolayer transition metal dichalcogenide semiconductors. Nat. Commun. 8, 1166 (2017).

43. Chernikov, A., Ruppert, C., Hill, H. M., Rigosi, A. F. & Heinz, T. F. Population inversion and giant bandgap renormalization in atomically thin WS2 layers. Nat. Photon. 9, 466–470 (2015).

44. Liang, Y. & Yang, L. Carrier plasmon induced nonlinear band gap renormalization in two-dimensional semiconductors. Phys. Rev. Lett. 114, 063001 (2015).

45. Liu, J., Zhang, X. & Lu, G. Excitonic effect drives ultrafast dynamics in van der Waals heterostructures. Nano Lett. 20, 4631–4637 (2020).

46. Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

47. Grimme, S. Semiempirical GGA-type density functional constructed with a long-range dispersion correction. J. Comput. Chem. 27, 1787–1799 (2006).

48. Maity, I., Naik, M. H., Maiti, P. K., Krishnamurthy, H. R. & Jain, M. Phonons in twisted transition-metal dichalcogenide bilayers: ultrasoft phasons and a transition from a superlubric to a pinned phase. Phys. Rev. Research 2, 013335 (2020).

49. Poncé, S., Margine, E. R., Verdi, C. & Giustino, F. EPW: electron–phonon coupling, transport and superconducting properties using maximally localized Wannier functions. Comput. Phys. Commun. 209, 116–133 (2016).

## Acknowledgements

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).

## Author information

Authors

### Contributions

A.S., A.R. and A.M.L. conceived the experiments. A.R. supervised the project. J.C. and A.R. prepared the heterostructures with inputs from E.C.R. A.S., J.C. and A.R. performed the UED experiments with support from A.H.M.R., X.S., M.E.Z., J.Y., X.W. and A.M.L. A.S. and J.C. analysed the UED data. A.S. performed the thermal transport calculations. F.H.J. designed the theoretical approach. J.B.H. and E.A.P. carried out the first-principles calculations with supervision from F.H.J. and inputs from J.B.N. E.B. performed the absorption and PL measurements under the supervision of T.F.H. J.D.G. performed the molecular dynamics simulations of thermal transport under the supervision of F.H.J. T.T. and K.W. grew the hBN crystals. A.S. and J.B.H. prepared the initial draft with significant contributions from E.A.P., F.H.J. and A.R., and feedback from J.B.N., T.F.H. and A.M.L. All the authors commented on the manuscript and approved the final version.

### Corresponding authors

Correspondence to Aditya Sood, Aaron M. Lindenberg, Felipe H. da Jornada or Archana Raja.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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### Peer review information

Nature Nanotechnology thanks Xiangfan Xu, Jin Zhao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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## Supplementary information

### Supplementary Information

Supplementary Figs. 1–18 and Sections 1–5.

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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

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• DOI: https://doi.org/10.1038/s41565-022-01253-7