Imaging moiré excited states with photocurrent tunnelling microscopy
Source abstract
Abstract
Moiré superlattices provide a highly tuneable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators to moiré excitons. Scanning tunnelling microscopy has played a key role in probing microscopic behaviours of the moiré correlated ground states at the atomic scale. However, imaging of quantum excited states in moiré heterostructures remains an outstanding challenge. Here we develop a photocurrent tunnelling microscopy technique that combines laser excitation and scanning tunnelling spectroscopy to directly visualize the electron and hole distribution within the photoexcited moiré exciton in twisted bilayer WS2. The tunnelling photocurrent alternates between positive and negative polarities at different locations within a single moiré unit cell. This alternating photocurrent originates from the in-plane charge transfer moiré exciton in twisted bilayer WS2, predicted by our GW-Bethe-Salpeter equation calculations, that emerges from the competition between the electron-hole Coulomb interaction and the moiré potential landscape. Our technique enables the exploration of photoexcited non-equilibrium moiré phenomena at the atomic scale.
Source: europepmc · Quality: candidate unverified · Source record ↗
Research context
OpenAlex topics: Quantum and electron transport phenomena · Molecular Junctions and Nanostructures · Semiconductor Quantum Structures and Devices
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (45)
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1. Li, H. et al. Imaging two-dimensional generalized Wigner crystals. Nature 597, 650–654 (2021).10.1038/s41586-021-03874-9 ↗
2. Regan, E. C. et al. Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices. Nature 579, 359–363 (2020).10.1038/s41586-020-2092-4 ↗
3. Xu, Y. et al. Correlated insulating states at fractional fillings of moiré superlattices. Nature 587, 214–218 (2020).10.1038/s41586-020-2868-6 ↗
4. Huang, X. et al. Correlated insulating states at fractional fillings of the WS2/WSe2 moiré lattice. Nat. Phys. 17, 715–719 (2021).10.1038/s41567-021-01171-w ↗
5. Xie, Y.-M., Zhang, C.-P., Hu, J.-X., Mak, K. F. & Law, K. T. Valley-polarized quantum anomalous Hall state in moiré MoTe2/WSe2 heterobilayers. Phys. Rev. Lett. 128, 026402 (2022).10.1103/PhysRevLett.128.026402 ↗
6. Li, T. et al. Quantum anomalous Hall effect from intertwined moiré bands. Nature 600, 641–646 (2021).10.1038/s41586-021-04171-1 ↗
7. Jin, C. et al. Observation of moiré excitons in WSe2/WS2 heterostructure superlattices. Nature 567, 76–80 (2019).10.1038/s41586-019-0976-y ↗
8. Naik, M. H. et al. Intralayer charge-transfer moiré excitons in van der Waals superlattices. Nature 609, 52–57 (2022).10.1038/s41586-022-04991-9 ↗
9. Seyler, K. L. et al. Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers. Nature 567, 66–70 (2019).10.1038/s41586-019-0957-1 ↗
10. Tran, K. et al. Evidence for moiré excitons in van der Waals heterostructures. Nature 567, 71–75 (2019).10.1038/s41586-019-0975-z ↗
11. Choi, Y. et al. Correlation-driven topological phases in magic-angle twisted bilayer graphene. Nature 589, 536–541 (2021).10.1038/s41586-020-03159-7 ↗
12. Kerelsky, A. et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 572, 95–100 (2019).10.1038/s41586-019-1431-9 ↗
13. Jiang, Y. et al. Charge order and broken rotational symmetry in magic-angle twisted bilayer graphene. Nature 573, 91–95 (2019).10.1038/s41586-019-1460-4 ↗
14. Wong, D. et al. Cascade of electronic transitions in magic-angle twisted bilayer graphene. Nature 582, 198–202 (2020).10.1038/s41586-020-2339-0 ↗
15. Xie, Y. et al. Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene. Nature 572, 101–105 (2019).10.1038/s41586-019-1422-x ↗
16. Cao, Y. et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Nature 556, 80–84 (2018).10.1038/nature26154 ↗
17. Li, H. et al. Mapping charge excitations in generalized Wigner crystals. Preprint at arXiv https://doi.org/10.48550/arXiv.2209.12830 (2022).10.48550/arXiv.2209.12830 ↗
18. Kim, H. et al. Evidence for unconventional superconductivity in twisted trilayer graphene. Nature 606, 494–500 (2022).10.1038/s41586-022-04715-z ↗
19. Oh, M. et al. Evidence for unconventional superconductivity in twisted bilayer graphene. Nature 600, 240–245 (2021).10.1038/s41586-021-04121-x ↗
20. Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).10.1038/nature26160 ↗
21. Karni, O. et al. Structure of the moiré exciton captured by imaging its electron and hole. Nature 603, 247–252 (2022).10.1038/s41586-021-04360-y ↗
22. Wang, L. et al. Correlated electronic phases in twisted bilayer transition metal dichalcogenides. Nat. Mater. 19, 861–866 (2020).10.1038/s41563-020-0708-6 ↗
23. Yankowitz, M. et al. Tuning superconductivity in twisted bilayer graphene. Science 363, 1059–1064 (2019).10.1126/science.aav1910 ↗
24. Li, H. et al. Imaging local discharge cascades for correlated electrons in WS2/WSe2 moiré superlattices. Nat. Phys. https://doi.org/10.1038/s41567-021-01324-x (2021).10.1038/s41567-021-01324-x ↗
25. Imai-Imada, M. et al. Orbital-resolved visualization of single-molecule photocurrent channels. Nature 603, 829–834 (2022).10.1038/s41586-022-04401-0 ↗
26. Wang, L., Xia, Y. & Ho, W. Atomic-scale quantum sensing based on the ultrafast coherence of an H2 molecule in an STM cavity. Science 376, 401–405 (2022).10.1126/science.abn9220 ↗
27. Qiu, X., Nazin, G. & Ho, W. Vibrationally resolved fluorescence excited with submolecular precision. Science 299, 542–546 (2003).10.1126/science.1078675 ↗
28. Ćavar, E. et al. Fluorescence and phosphorescence from individual C60 molecules excited by local electron tunneling. Phys. Rev. Lett. 95, 196102 (2005).10.1103/PhysRevLett.95.196102 ↗
29. Bolotov, L., Tada, T., Poborchii, V., Fukuda, K. & Kanayama, T. Spatial distribution of photocurrent in Si stripes under tilted illumination measured by multimode scanning probe microscopy. Jpn J. Appl. Phys. 51, 088005 (2012).10.1143/JJAP.51.088005 ↗
30. Yamamoto, H. Y. H., Kamiya, I. K. I. & Takahashi, T. T. T. Photoinduced current properties of InAs-covered GaAs studied by scanning tunneling microscopy. Jpn J. Appl. Phys. 38, 3871 (1999).10.1143/JJAP.38.3871 ↗
31. Takeuchi, O. et al. Probing subpicosecond dynamics using pulsed laser combined scanning tunneling microscopy. Appl. Phys. Lett. 85, 3268–3270 (2004).10.1063/1.1804238 ↗
32. McEllistrem, M., Haase, G., Chen, D. & Hamers, R. Electrostatic sample–tip interactions in the scanning tunneling microscope. Phys. Rev. Lett. 70, 2471 (1993).10.1103/PhysRevLett.70.2471 ↗
33. Kochanski, G. P. & Bell, R. STM measurements of photovoltage on Si(111) and Si(111):Ge. Surf. Sci. 273, L435–L440 (1992).10.1016/0039-6028(92)90266-9 ↗
34. Matthes, T. W. et al. Investigation of photoinduced tunneling current and local surface photovoltage by STM. Appl. Surf. Sci. 123, 187–191 (1998).10.1016/S0169-4332(97)00480-7 ↗
35. Li, H. et al. Imaging moiré flat bands in three-dimensional reconstructed WSe2/WS2 superlattices. Nat. Mater. 20, 945–950 (2021).10.1038/s41563-021-00923-6 ↗
36. Naik, M. H. & Jain, M. Ultraflatbands and shear solitons in moiré patterns of twisted bilayer transition metal dichalcogenides. Phys. Rev. Lett. 121, 266401 (2018).10.1103/PhysRevLett.121.266401 ↗
37. Naik, M. H., Kundu, S., Maity, I. & Jain, M. Origin and evolution of ultraflat bands in twisted bilayer transition metal dichalcogenides: realization of triangular quantum dots. Phys. Rev. B 102, 075413 (2020).10.1103/PhysRevB.102.075413 ↗
38. Wu, F., Lovorn, T. & MacDonald, A. H. Topological exciton bands in moiré heterojunctions. Phys. Rev. Lett. 118, 147401 (2017).10.1103/PhysRevLett.118.147401 ↗
39. Jin, C. et al. Ultrafast dynamics in van der Waals heterostructures. Nat. Nanotechnol. 13, 994–1003 (2018).10.1038/s41565-018-0298-5 ↗
40. Wang, H., Zhang, C. & Rana, F. Ultrafast dynamics of defect-assisted electron–hole recombination in monolayer MoS2. Nano Lett. 15, 339–345 (2015).10.1021/nl503636c ↗
41. Shi, H. et al. Exciton dynamics in suspended monolayer and few-layer MoS2 2D crystals. ACS Nano 7, 1072–1080 (2013).10.1021/nn303973r ↗
42. Jauregui, L. A. et al. Electrical control of interlayer exciton dynamics in atomically thin heterostructures. Science 366, 870–875 (2019).10.1126/science.aaw4194 ↗
43. Hybertsen, M. S. & Louie, S. G. Electron correlation in semiconductors and insulators: band gaps and quasiparticle energies. Phys. Rev. B 34, 5390–5413 (1986).10.1103/PhysRevB.34.5390 ↗
44. Rohlfing, M. & Louie, S. G. Electron–hole excitations in semiconductors and insulators. Phys. Rev. Lett. 81, 2312–2315 (1998).10.1103/PhysRevLett.81.2312 ↗
45. Wang, L. et al. One-dimensional electrical contact to a two-dimensional material. Science 342, 614–617 (2013).10.1126/science.1244358 ↗