Dissecting intervalley coupling mechanisms in monolayer transition metal dichalcogenides
Source abstract
Abstract
Monolayer (1L) transition metal dichalcogenides (TMDs) provide a unique opportunity to control the valley degree of freedom of optically excited charge carriers due to the spin-valley locking effect. However, a unified picture of competing intervalley coupling processes in 1L-TMDs is lacking. Here, we apply broadband helicity-resolved transient absorption to explore exciton valley polarization dynamics in 1L-WSe2. By combining experimental results with microscopic simulations, we dissect individual intervalley coupling mechanisms and reveal the crucial role of phonon-assisted scattering in the fast decay of the A exciton circular dichroism and the formation of the dichroism of opposite polarity for the B exciton. We further provide a consistent description of the valley depolarization driven by an intervalley-exchange-activating momentum-dark Dexter process and indicate the presence of efficient single electron spin-flip mechanisms. Our study advances understanding of exciton dynamics in TMDs.
Source: openalex_inverted_index · Quality: baseline
Research context
OpenAlex topics: 2D Materials and Applications · Graphene research and applications · Photochromic and Fluorescence Chemistry
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (71)
Show source-provided references
1. Xiao, D., Liu, G. B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).10.1103/PhysRevLett.108.196802 ↗
2. Xu, X., Yao, W., Xiao, D. & Heinz, T. F. Spin and pseudospins in layered transition metal dichalcogenides. Nat. Phys. 10, 343–350 (2014).10.1038/nphys2942 ↗
3. Schaibley, J. R. et al. Valleytronics in 2D materials. Nat. Rev. Mater. 1, 16055 (2016).10.1038/natrevmats.2016.55 ↗
4. Liu, Y. et al. Valleytronics in transition metal dichalcogenides materials. Nano Res. 12, 2695–2711 (2019).10.1007/s12274-019-2497-2 ↗
5. Siwen, Z. et al. Valley manipulation in monolayer transition metal dichalcogenides and their hybrid systems: status and challenges. Rep. Prog. Phys. 84, 026401 (2021).10.1088/1361-6633/abdb98 ↗
6. Chernikov, A. et al. Exciton binding energy and nonhydrogenic rydberg series in monolayer WS2. Phys. Rev. Lett. 113, 076802 (2014).10.1103/PhysRevLett.113.076802 ↗
7. Sallen, G. et al. Robust optical emission polarization in MoS2 monolayers through selective valley excitation. Phys. Rev. B 86, 081301 (2012).10.1103/PhysRevB.86.081301 ↗
8. Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nat. Nanotechnol. 7, 490–493 (2012).10.1038/nnano.2012.95 ↗
9. Mak, K. F., Xiao, D. & Shan, J. Light–valley interactions in 2D semiconductors. Nat. Photonics 12, 451–460 (2018).10.1038/s41566-018-0204-6 ↗
10. Dal Conte, S., Trovatello, C., Gadermaier, C. & Cerullo, G. Ultrafast photophysics of 2D semiconductors and related heterostructures. Trends Chem. 2, 28–42 (2020).10.1016/j.trechm.2019.07.007 ↗
11. Zhu, C. R. et al. Exciton valley dynamics probed by Kerr rotation in WSe2 monolayers. Phys. Rev. B 90, 161302 (2014).10.1103/PhysRevB.90.161302 ↗
12. Plechinger, G. et al. Valley dynamics of excitons in monolayer dichalcogenides. Phys. Status Solidi (RRL) - Rapid Res. Lett. 11, 1700131 (2017).10.1002/pssr.201700131 ↗
13. Mai, C. et al. Many-body effects in valleytronics: direct measurement of valley lifetimes in single-layer MoS2. Nano Lett. 14, 202–206 (2014).10.1021/nl403742j ↗
14. Mai, C. et al. Exciton valley relaxation in a single layer of WS2 measured by ultrafast spectroscopy. Phys. Rev. B 90, 041414 (2014).10.1103/PhysRevB.90.041414 ↗
15. Wang, Z. et al. Intravalley spin-flip relaxation dynamics in single-layer WS2. Nano Lett. 18, 6882–6891 (2018).10.1021/acs.nanolett.8b02774 ↗
16. Lloyd, L. T. et al. Sub-10 fs intervalley exciton coupling in monolayer MoS2 revealed by helicity-resolved two-dimensional electronic spectroscopy. ACS Nano 15, 10253–10263 (2021).10.1021/acsnano.1c02381 ↗
17. Schmidt, R. et al. Ultrafast coulomb-induced intervalley coupling in atomically thin WS2. Nano Lett. 16, 2945–2950 (2016).10.1021/acs.nanolett.5b04733 ↗
18. Berghäuser, G. et al. Inverted valley polarization in optically excited transition metal dichalcogenides. Nat. Commun. 9, 971 (2018).10.1038/s41467-018-03354-1 ↗
19. Selig, M. et al. Ultrafast dynamics in monolayer transition metal dichalcogenides: interplay of dark excitons, phonons, and intervalley exchange. Phys. Rev. Res. 1, 022007 (2019).10.1103/PhysRevResearch.1.022007 ↗
20. Yu, T. & Wu, M. Valley depolarization due to intervalley and intravalley electron-hole exchange interactions in monolayer MoS2. Phys. Rev. B 89, 205303 (2014).10.1103/PhysRevB.89.205303 ↗
21. Combescot, M., Amand, T. & Shiau, S.-Y. Ab initio quantum approach to electron-hole exchange for semiconductors hosting Wannier excitons. Phys. Rev. B 107, 115206 (2023).10.1103/PhysRevB.107.115206 ↗
22. Kioseoglou, G., Hanbicki, A. T., Currie, M., Friedman, A. L. & Jonker, B. T. Optical polarization and intervalley scattering in single layers of MoS2 and MoSe2. Sci. Rep. 6, 25041 (2016).10.1038/srep25041 ↗
23. Molina-Sánchez, A., Sangalli, D., Wirtz, L. & Marini, A. Ab initio calculations of ultrashort carrier dynamics in two-dimensional materials: valley depolarization in single-layer WSe2. Nano Lett. 17, 4549–4555 (2017).10.1021/acs.nanolett.7b00175 ↗
24. Carvalho, B. R. et al. Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy. Nat. Commun. 8, 14670 (2017).10.1038/ncomms14670 ↗
25. Brem, S. et al. Phonon-assisted photoluminescence from indirect excitons in monolayers of transition-metal dichalcogenides. Nano Lett. 20, 2849–2856 (2020).10.1021/acs.nanolett.0c00633 ↗
26. He, M. et al. Valley phonons and exciton complexes in a monolayer semiconductor. Nat. Commun. 11, 618 (2020).10.1038/s41467-020-14472-0 ↗
27. Bae, S. et al. K-point longitudinal acoustic phonons are responsible for ultrafast intervalley scattering in monolayer MoSe2. Nat. Commun. 13, 4279 (2022).10.1038/s41467-022-32008-6 ↗
28. Selig, M. et al. Dark and bright exciton formation, thermalization, and photoluminescence in monolayer transition metal dichalcogenides. 2D Mater. 5, 035017 (2018).10.1088/2053-1583/aabea3 ↗
29. Bernal-Villamil, I. et al. Exciton broadening and band renormalization due to Dexter-like intervalley coupling. 2D Mater. 5, 025011 (2018).10.1088/2053-1583/aaaa8b ↗
30. Guo, L. et al. Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides. Nat. Phys. 15, 228–232 (2019).10.1038/s41567-018-0362-y ↗
31. Huang, J., Hoang, T. B., Ming, T., Kong, J. & Mikkelsen, M. H. Temporal and spatial valley dynamics in two-dimensional semiconductors probed via Kerr rotation. Phys. Rev. B 95, 075428 (2017).10.1103/PhysRevB.95.075428 ↗
32. Koutenský, P. et al. Ultrafast dynamics of valley-polarized excitons in WSe2 monolayer studied by few-cycle laser pulses. Nanomaterials 13, 1207 (2023).10.3390/nano13071207 ↗
33. Raiber, S. et al. Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2. Nat. Commun. 13, 4997 (2022).10.1038/s41467-022-32534-3 ↗
34. Ivanov, A. L. & Haug, H. Self-consistent theory of the biexciton optical nonlinearity. Phys. Rev. B 48, 1490–1504 (1993).10.1103/PhysRevB.48.1490 ↗
35. Katsch, F., Selig, M., Carmele, A. & Knorr, A. Theory of exciton-exciton interactions in monolayer transition metal dichalcogenides. Phys. Status Solidi 255, 1800185 (2018).10.1002/pssb.201800185 ↗
36. Sie, E. J., Frenzel, A. J., Lee, Y.-H., Kong, J. & Gedik, N. Intervalley biexcitons and many-body effects in monolayer MoS2. Phys. Rev. B 92, 125417 (2015).10.1103/PhysRevB.92.125417 ↗
37. Deckert, T. et al. Coherent coulomb intra- and intervalley many-body effects in single-layer transition metal dichalcogenides. Phys. Rev. Lett. 135, 066902 (2025).10.1103/j5cv-rffq ↗
38. Kumar, N. et al. Exciton-exciton annihilation in MoSe2 monolayers. Phys. Rev. B 89, 125427 (2014).10.1103/PhysRevB.89.125427 ↗
39. Seo, M. et al. Ultrafast optical microscopy of single monolayer molybdenum disulfide flakes. Sci. Rep. 6, 21601 (2016).10.1038/srep21601 ↗
40. Dal Conte, S. et al. Ultrafast valley relaxation dynamics in monolayer MoS2 probed by nonequilibrium optical techniques. Phys. Rev. B 92, 235425 (2015).10.1103/PhysRevB.92.235425 ↗
41. Mahmood, F., Alpichshev, Z., Lee, Y.-H., Kong, J. & Gedik, N. Observation of exciton-exciton interaction mediated valley depolarization in monolayer MoSe2. Nano Lett. 18, 223–228 (2018).10.1021/acs.nanolett.7b03953 ↗
42. 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. Photonics 9, 466–470 (2015).10.1038/nphoton.2015.104 ↗
43. Dendzik, M. et al. Observation of an excitonic Mott transition through ultrafast core-cum-conduction photoemission spectroscopy. Phys. Rev. Lett. 125, 096401 (2020).10.1103/PhysRevLett.125.096401 ↗
44. Hsu, W.-T. et al. Optically initialized robust valley-polarized holes in monolayer WSe2. Nat. Commun. 6, 8963 (2015).10.1038/ncomms9963 ↗
45. Fricke, J. Transport equations including many-particle correlations for an arbitrary quantum system: a general formalism. Ann. Phys. 252, 479–498 (1996).10.1006/aphy.1996.0142 ↗
46. Katsch, F., Selig, M. & Knorr, A. Exciton-scattering-induced dephasing in two-dimensional semiconductors. Phys. Rev. Lett. 124, 257402 (2020).10.1103/PhysRevLett.124.257402 ↗
47. Trovatello, C. et al. Disentangling many-body effects in the coherent optical response of 2D semiconductors. Nano Lett. 22, 5322–5329 (2022).10.1021/acs.nanolett.2c01309 ↗
48. Katsch, F., Selig, M. & Knorr, A. Theory of coherent pump–probe spectroscopy in monolayer transition metal dichalcogenides. 2D Mater. 7, 015021 (2019).10.1088/2053-1583/ab5407 ↗
49. Katzer, M. et al. Exciton-phonon scattering: competition between the bosonic and fermionic nature of bound electron-hole pairs. Phys. Rev. B 108, L121102 (2023).10.1103/PhysRevB.108.L121102 ↗
50. Policht, V. R. et al. Time-domain observation of interlayer exciton formation and thermalization in a MoSe2/WSe2 heterostructure. Nat. Commun. 14, 7273 (2023).10.1038/s41467-023-42915-x ↗
51. Thränhardt, A., Kuckenburg, S., Knorr, A., Meier, T. & Koch, S. Quantum theory of phonon-assisted exciton formation and luminescence in semiconductor quantum wells. Phys. Rev. B 62, 2706 (2000).10.1103/PhysRevB.62.2706 ↗
52. Maialle, M. Z., de Andrada e Silva, E.A. & Sham, L. Exciton spin dynamics in quantum wells. Phys. Rev. B 47, 15776 (1993).10.1103/PhysRevB.47.15776 ↗
53. Selig, M. et al. Suppression of intervalley exchange coupling in the presence of momentum-dark states in transition metal dichalcogenides. Phys. Rev. Res. 2, 023322 (2020).10.1103/PhysRevResearch.2.023322 ↗
54. Jasiński, J. et al. Control of the valley polarization of monolayer WSe2 by Dexter-like coupling. 2D Mater 11, 025007 (2024).10.1088/2053-1583/ad1ae8 ↗
55. Winkler, R. Spin-orbit Coupling Effects in Two-Dimensional Electron and Hole Systems (Springer Berlin, 2003).10.1007/b13586 ↗
56. Mittenzwey, H. et al. Ultrafast optical control of rashba interactions in a TMDC heterostructure. Phys. Rev. Lett. 134, 026901 (2025).10.1103/PhysRevLett.134.026901 ↗
57. Mittenzwey, H. & Knorr, A. Many-body Rashba spin-orbit interaction and exciton spin relaxation in atomically thin semiconductor structures. Preprint at https://doi.org/10.48550/arXiv.2509.04285 (2025).10.48550/arXiv.2509.04285 ↗
58. Slobodeniuk, A. & Basko, D. Spin-flip processes and radiative decay of dark intravalley excitons in transition metal dichalcogenide monolayers. 2D Mater 3, 035009 (2016).10.1088/2053-1583/3/3/035009 ↗
59. Zhuang, X., He, B., Javvaji, B. & Park, H. S. Intrinsic bending flexoelectric constants in two-dimensional materials. Phys. Rev. B 99, 054105 (2019).10.1103/PhysRevB.99.054105 ↗
60. Schlipf, M. & Giustino, F. Dynamic Rashba-Dresselhaus effect. Phys. Rev. Lett. 127, 237601 (2021).10.1103/PhysRevLett.127.237601 ↗
61. Lagarde, D. et al. Efficient electron spin relaxation by chiral phonons in WSe2 monolayers. Phys. Rev. B 110, 195403 (2024).10.1103/PhysRevB.110.195403 ↗
62. Chan, Y. -h. et al. Exciton thermalization dynamics in monolayer MoS2: a first-principles Boltzmann equation study. Phys. Rev. B 111, 184305 (2025).10.1103/PhysRevB.111.184305 ↗
63. Zhang, X.-W. & Cao, T. Ab initio calculations of spin-nonconserving exciton–phonon scattering in monolayer transition metal dichalcogenides. J. Phys. Condens. Matter 34, 264002 (2022).10.1088/1361-648X/ac6649 ↗
64. Kormányos, A. et al. k⋅p theory for two-dimensional transition metal dichalcogenide semiconductors. 2D Mater. 2, 022001 (2015).10.1088/2053-1583/2/2/022001 ↗
65. Liu, G.-B., Shan, W.-Y., Yao, Y., Yao, W. & Xiao, D. Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides. Phys. Rev. B 88, 085433 (2013).10.1103/PhysRevB.88.085433 ↗
66. Maja, F., Samuel, B., August, E. & Ermin, M. Brightening of spin- and momentum-dark excitons in transition metal dichalcogenides. 2D Mater. 8, 015013 (2020).
67. Jeong, T.-Y. et al. Valley depolarization in monolayer transition-metal dichalcogenides with zone-corner acoustic phonons. Nanoscale 12, 22487–22494 (2020).10.1039/D0NR04761A ↗
68. Liu, F. et al. Disassembling 2D van der Waals crystals into macroscopic monolayers and reassembling into artificial lattices. Science 367, 903–906 (2020).10.1126/science.aba1416 ↗
69. Mkrtchian, G. F., Knorr, A. & Selig, M. Theory of second-order excitonic nonlinearities in transition metal dichalcogenides. Phys. Rev. B 100, 125401 (2019).10.1103/PhysRevB.100.125401 ↗
70. Knorr, A., Hughes, S., Stroucken, T. & Koch, S. Theory of ultrafast spatio-temporal dynamics in semiconductor heterostructures. Chem. Phys. 210, 27–47 (1996).10.1016/0301-0104(96)00120-6 ↗
71. Jahnke, F., Kira, M. & Koch, S. Linear and nonlinear optical properties of excitons in semiconductor quantum wells and microcavities. Z. Phys. B Condens. Matter 104, 559–572 (1997).10.1007/s002570050490 ↗