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  • Technical Review
  • Published:

Guide to optical spectroscopy of layered semiconductors

Nature Reviews Physics volume 3, pages 39–54 (2021)Cite this article

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Abstract

Potential applications in photonics and optoelectronics are based on our understanding of the light–matter interaction on an atomic monolayer scale. Atomically thin 2D transition metal dichalcogenides, such as MoS2 and WSe2, are model systems for layered semiconductors with a bandgap in the visible region of the optical spectrum. They can be assembled to form heterostructures and combine the unique properties of the constituent monolayers. In this Technical Review, we provide an introduction to optical spectroscopy for layered materials as a powerful, non-invasive tool to access details of the electronic band structure and crystal quality. We discuss the physical origin of the main absorption and emission features in the optical spectra and how they can be tuned. We explain key aspects of practical set-ups for performing experiments in different conditions and the important influence of the direct sample environment, such as substrates and encapsulation layers, on the emission and absorption mechanisms. A survey of optical techniques that probe the coupling between layers and analyse carrier polarization dynamics for spin- and valleytronics is provided.

Key points

  • Optical spectroscopy tools give access to details of the electronic band structure, crystal quality, crystal orientation, light–matter interaction and spin–valley polarization of 2D materials.

  • Key experimental parameters such as temperature, applied electric and magnetic fields, optical excitation power and the direct sample environment (such as substrate and encapsulation layers) strongly influence optical absorption and emission.

  • To achieve high spatial resolution, experiments on layered materials are carried out in optical microscopes. The high numerical aperture of the microscope objectives results in excitation and collection of light away from normal incidence, which gives access to information on optical transitions with different spatial orientations of the optical dipole.

  • In layered materials with strong excitonic effects, light–matter interaction is enhanced at specific energies. The emission as well as the absorption is therefore strongly energy-dependent, and light sources with tunable excitation provide flexibility for controlling optical absorption in the sample.

  • Using optical excitations with well-defined light polarization enables the excitation of carriers with specific spin and/or valley quantum numbers determined by the optical selection rules in the crystal. This reveals important information on the spin and valley dynamics in the material.

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Fig. 1: Excitons in transition metal dichalcogenide monolayers and heterobilayers for optical spectroscopy.
Fig. 2: Variation in photoluminescence response for different experimental conditions.
Fig. 3: Moiré interlayer excitons in heterobilayers.

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References

  1. Ubrig, N. et al. Design of van der Waals interfaces for broad-spectrum optoelectronics. Nat. Mater. 19, 299–304 (2020).

    ADS  Google Scholar 

  2. Mounet, N. et al. Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds. Nat. Nanotechnol. 13, 246–252 (2018).

    ADS  Google Scholar 

  3. Seyler, K. L. et al. Signatures of moiré-trapped valley excitons in MoSe2/ WSe2 heterobilayers. Nature 567, 66–70 (2019).

    ADS  Google Scholar 

  4. Shimazaki, Y. et al. Strongly correlated electrons and hybrid excitons in a moiré heterostructure. Nature 580, 472–477 (2020).

    ADS  Google Scholar 

  5. Sun, Z. et al. Giant nonreciprocal second-harmonic generation from antiferromagnetic bilayer CrI3. Nature 572, 497–501 (2019).

    ADS  Google Scholar 

  6. Ubrig, N. et al. Low-temperature monoclinic layer stacking in atomically thin CrI3 crystals. 2D Mater. 7, 015007 (2019).

    Google Scholar 

  7. Mak, K. F., Shan, J. & Ralph, D. C. Probing and controlling magnetic states in 2D layered magnetic materials. Nat. Rev. Phys. 1, 646–661 (2019).

    Google Scholar 

  8. Zhong, D. et al. Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics. Sci. Adv. 3, e1603113 (2017).

    ADS  Google Scholar 

  9. Ciorciaro, L., Kroner, M., Watanabe, K., Taniguchi, T. & Imamoglu, A. Observation of magnetic proximity effect using resonant optical spectroscopy of an electrically tunable MoSe2/CrBr3 heterostructure. Phys. Rev. Lett. 124, 197401 (2020).

    ADS  Google Scholar 

  10. Lyons, T. P. et al. Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures. Nat. Commun. 11, 6021 (2020).

    Google Scholar 

  11. Sortino, L. et al. Enhanced light–matter interaction in an atomically thin semiconductor coupled with dielectric nano-antennas. Nat. Commun. 10, 5119 (2019).

    ADS  Google Scholar 

  12. Paik, E. Y. et al. Interlayer exciton laser of extended spatial coherence in atomically thin heterostructures. Nature 576, 80–84 (2019).

    ADS  Google Scholar 

  13. Zhang, C. et al. Interlayer couplings, Moiré patterns, and 2D electronic superlattices in MoS2/WSe2 hetero-bilayers. Sci. Adv. 3, e1601459 (2017).

    ADS  Google Scholar 

  14. Sushko, A. et al. High resolution imaging of reconstructed domains and moiré patterns in functional van der Waals heterostructure devices. Preprint at https://arxiv.org/abs/1912.07446 (2019).

  15. Andersen, T. I. et al. Moiré excitons correlated with superlattice structure in twisted WSe2/WSe2 homobilayers. Preprint at https://arxiv.org/abs/1912.06955 (2019).

  16. Shree, S. et al. High optical quality of MoS2 monolayers grown by chemical vapor deposition. 2D Mater. 7, 015011 (2019).

    Google Scholar 

  17. Holler, J. et al. Low-frequency Raman scattering in WSe2–MoSe2 heterobilayers: evidence for atomic reconstruction. Appl. Phys. Lett. 117, 013104 (2020). A study that shows evidence of atomic reconstruction and stacking order in heterobilayers by means of low-frequency Raman spectroscopy.

    ADS  Google Scholar 

  18. Zhao, Y., Ippolito, S. & Samorì, P. Functionalization of 2D materials with photosensitive molecules: from light-responsive hybrid systems to multifunctional devices. Adv. Opt. Mater. 7, 1900286 (2019).

    Google Scholar 

  19. Mak, K. F. & Shan, J. Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides. Nat. Photonics 10, 216–226 (2016).

    ADS  Google Scholar 

  20. Yang, L. et al. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2. Nat. Phys. 11, 830–834 (2015).

    Google Scholar 

  21. Hsu, W.-T. et al. Optically initialized robust valley-polarized holes in monolayer WSe2. Nat. Commun. 6, 8963 (2015).

    ADS  Google Scholar 

  22. Dey, P. et al. Gate-controlled spin–valley locking of resident carriers in WSe2 monolayers. Phys. Rev. Lett. 119, 137401 (2017).

    ADS  Google Scholar 

  23. Branny, A., Kumar, S., Proux, R. & Gerardot, B. D. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor. Nat. Commun. 8, 15053 (2017).

    ADS  Google Scholar 

  24. Palacios-Berraquero, C. et al. Large-scale quantum-emitter arrays in atomically thin semiconductors. Nat. Commun. 8, 15093 (2017).

    ADS  Google Scholar 

  25. Horng, J. et al. Perfect absorption by an atomically thin crystal. Phys. Rev. Appl. 14, 024009 (2020).

    ADS  Google Scholar 

  26. Scuri, G. et al. Large excitonic reflectivity of monolayer MoSe2 encapsulated in hexagonal boron nitride. Phys. Rev. Lett. 120, 037402 (2018).

    ADS  Google Scholar 

  27. Back, P., Zeytinoglu, S., Ijaz, A., Kroner, M. & Imamoğlu, A. Realization of an electrically tunable narrow-bandwidth atomically thin mirror using monolayer MoSe2. Phys. Rev. Lett. 120, 037401 (2018).

    ADS  Google Scholar 

  28. Epstein, I. et al. Near-unity light absorption in a monolayer WS2 van der Waals heterostructure cavity. Nano Lett. 20, 3545–3552 (2020).

    ADS  Google Scholar 

  29. Jiang, S., Li, L., Wang, Z., Mak, K. F. & Shan, J. Controlling magnetism in 2D CrI3 by electrostatic doping. Nat. Nanotechnol. 13, 549–553 (2018).

    ADS  Google Scholar 

  30. Frindt, R. Single crystals of MoS2 several molecular layers thick. J. Appl. Phys. 37, 1928–1929 (1966).

    ADS  Google Scholar 

  31. Dickinson, R. G. & Pauling, L. The crystal structure of molybdenite. J. Am. Chem. Soc. 45, 1466–1471 (1923).

    Google Scholar 

  32. Wilson, J. A. & Yoffe, A. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 18, 193–335 (1969).

    ADS  Google Scholar 

  33. Van Baren, J. et al. Stacking-dependent interlayer phonons in 3R and 2H MoS2. 2D Mater. 6, 025022 (2019).

    ADS  Google Scholar 

  34. Frondel, J. W. & Wickman, F. E. Molybdenite polytypes in theory and occurrence. ii. some naturally-occurring polytypes of molybdenite. Am. Mineral. 55, 1857–1875 (1970).

    Google Scholar 

  35. 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).

    ADS  Google Scholar 

  36. Yu, H., Liu, G.-B., Tang, J., Xu, X. & Yao, W. Moiré excitons: from programmable quantum emitter arrays to spin–orbit-coupled artificial lattices. Sci. Adv. 3, e1701696 (2017).

    ADS  Google Scholar 

  37. Dyakonov, M. I. Spin Physics in Semiconductors, Vol. 1 (Springer, 2017).

  38. Mak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).

    ADS  Google Scholar 

  39. Splendiani, A. et al. Emerging photoluminescence in monolayer MoS2. Nano Lett. 10, 1271–1275 (2010).

    ADS  Google Scholar 

  40. Tonndorf, P. et al. Photoluminescence emission and Raman response of monolayer MoS2, MoSe2, and WSe2. Opt. Express 21, 4908–4916 (2013).

    ADS  Google Scholar 

  41. Moody, G. et al. Intrinsic homogeneous linewidth and broadening mechanisms of excitons in monolayer transition metal dichalcogenides. Nat. Commun. 6, 8315 (2015).

    ADS  Google Scholar 

  42. Wang, G. et al. Giant enhancement of the optical second-harmonic emission of WSe2 monolayers by laser excitation at exciton resonances. Phys. Rev. Lett. 114, 097403 (2015).

    ADS  Google Scholar 

  43. Kormányos, A. et al. k ⋅ p theory for two-dimensional transition metal dichalcogenide semiconductors. 2D Mater. 2, 022001 (2015).

    Google Scholar 

  44. He, K. et al. Tightly bound excitons in monolayer WSe2. Phys. Rev. Lett. 113, 026803 (2014).

    ADS  Google Scholar 

  45. Chernikov, A. et al. Exciton binding energy and nonhydrogenic Rydberg series in monolayer WS2. Phys. Rev. Lett. 113, 076802 (2014).

    ADS  Google Scholar 

  46. Ugeda, M. M. et al. Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nat. Mater. 13, 1091–1095 (2014).

    ADS  Google Scholar 

  47. Wang, G. et al. Colloquium: Excitons in atomically thin transition metal dichalcogenides. Rev. Mod. Phys. 90, 021001 (2018).

    ADS  MathSciNet  Google Scholar 

  48. Ramasubramaniam, A. Large excitonic effects in monolayers of molybdenum and tungsten dichalcogenides. Phys. Rev. B 86, 115409 (2012).

    ADS  Google Scholar 

  49. Song, Y. & Dery, H. Transport theory of monolayer transition-metal dichalcogenides through symmetry. Phys. Rev. Lett. 111, 026601 (2013).

    ADS  Google Scholar 

  50. Rytova, N. S. Screened potential of a point charge in a thin film. Preprint at https://arxiv.org/abs/1806.00976 (2018).

  51. Keldysh, L. V. Coulomb interaction in thin semiconductor and semimetal films. Sov. J. Exp. Theor. Phys. Lett. 29, 658 (1979).

    ADS  Google Scholar 

  52. Raja, A. et al. Coulomb engineering of the bandgap and excitons in two-dimensional materials. Nat. Commun. 8, 15251 (2017).

    ADS  Google Scholar 

  53. Waldecker, L. et al. Rigid band shifts in two-dimensional semiconductors through external dielectric screening. Phys. Rev. Lett. 123, 206403 (2019).

    ADS  Google Scholar 

  54. Rhodes, D., Chae, S. H., Ribeiro-Palau, R. & Hone, J. Disorder in van der Waals heterostructures of 2D materials. Nat. Mater. 18, 541 (2019).

    ADS  Google Scholar 

  55. Cadiz, F. et al. Excitonic linewidth approaching the homogeneous limit in MoS2-based van der Waals heterostructures. Phys. Rev. X 7, 021026 (2017).

    Google Scholar 

  56. Zhou, Y. et al. Probing dark excitons in atomically thin semiconductors via near-field coupling to surface plasmon polaritons. Nat. Nanotechnol. 12, 856–860 (2017).

    ADS  Google Scholar 

  57. Brotons-Gisbert, M. et al. Out-of-plane orientation of luminescent excitons in two-dimensional indium selenide. Nat. Commun. 10, 3913 (2019).

    ADS  Google Scholar 

  58. Wang, G. et al. In-plane propagation of light in transition metal dichalcogenide monolayers: optical selection rules. Phys. Rev. Lett. 119, 047401 (2017).

    ADS  Google Scholar 

  59. Robert, C. et al. Fine structure and lifetime of dark excitons in transition metal dichalcogenide monolayers. Phys. Rev. B 96, 155423 (2017).

    ADS  Google Scholar 

  60. Robert, C. et al. Measurement of the spin-forbidden dark excitons in MoS2 and MoSe2 monolayers. Nat. Commun. 11, 4037 (2020).

    ADS  Google Scholar 

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

    ADS  Google Scholar 

  62. Schmidt, P. et al. Nano-imaging of intersubband transitions in van der Waals quantum wells. Nat. Nanotechnol. 13, 1035–1041 (2018).

    ADS  Google Scholar 

  63. Liu, Y., Stradins, P. & Wei, S.-H. Van der Waals metal–semiconductor junction: weak Fermi level pinning enables effective tuning of Schottky barrier. Sci. Adv. 2, e1600069 (2016).

    ADS  Google Scholar 

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

    ADS  Google Scholar 

  65. Rivera, P. et al. Observation of long-lived interlayer excitons in monolayer MoSe2–WSe2 heterostructures. Nat. Commun. 6, 6242 (2015).

    ADS  Google Scholar 

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

    ADS  Google Scholar 

  67. Weston, A. et al. Atomic reconstruction in twisted bilayers of transition metal dichalcogenides. Nat. Nanotechnol. 15, 592–597 (2020).

    ADS  Google Scholar 

  68. Sung, J. et al. Broken mirror symmetry in excitonic response of reconstructed domains in twisted MoSe2/MoSe2 bilayers. Nat. Nanotechnol. 15, 750–754 (2020).

    ADS  Google Scholar 

  69. Regan, E. C. et al. Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices. Nature 579, 359–363 (2020).

    ADS  Google Scholar 

  70. Wang, Z. et al. Evidence of high-temperature exciton condensation in two-dimensional atomic double layers. Nature 574, 76–80 (2019).

    ADS  Google Scholar 

  71. Dau, M. T. et al. Beyond van der Waals interaction: the case of MoSe2 epitaxially grown on few-layer graphene. ACS Nano 12, 2319–2331 (2018).

    Google Scholar 

  72. Pacuski, W. Narrow excitonic lines and large-scale homogeneity of transition metal dichalcogenide monolayer grown by MBE on hBN. Nano Lett. 20, 3058–3066 (2020).

    ADS  Google Scholar 

  73. Amani, M. et al. Near-unity photoluminescence quantum yield in MoS2. Science 350, 1065–1068 (2015).

    ADS  Google Scholar 

  74. Lee, Y.-H. et al. Synthesis of large-area MoS2 atomic layers with chemical vapor deposition. Adv. Mater. 24, 2320–2325 (2012).

    Google Scholar 

  75. Kobayashi, Y. et al. Growth and optical properties of high-quality monolayer WS2 on graphite. ACS Nano 9, 4056–4063 (2015).

    Google Scholar 

  76. Rhyee, J.-S. et al. High-mobility transistors based on large-area and highly crystalline CVD-grown MoSe2 films on insulating substrates. Adv. Mater. 28, 2316–2321 (2016).

    Google Scholar 

  77. George, A. et al. Controlled growth of transition metal dichalcogenide monolayers using Knudsen-type effusion cells for the precursors. J. Phys. Mater. 2, 016001 (2019).

    Google Scholar 

  78. Sahoo, P. K., Memaran, S., Xin, Y., Balicas, L. & Gutiérrez, H. R. One-pot growth of two-dimensional lateral heterostructures via sequential edge-epitaxy. Nature 553, 63–67 (2018).

    ADS  Google Scholar 

  79. Li, J. et al. General synthesis of two-dimensional van der Waals heterostructure arrays. Nature 579, 368–374 (2020).

    ADS  Google Scholar 

  80. Jia, H. et al. Large-scale arrays of single-and few-layer MoS2 nanomechanical resonators. Nanoscale 8, 10677–10685 (2016).

    ADS  Google Scholar 

  81. Paradisanos, I. et al. Controlling interlayer excitons in MoS2 layers grown by chemical vapor deposition. Nat. Commun. 11, 2391 (2020).

    ADS  Google Scholar 

  82. Li, M.-Y. et al. Epitaxial growth of a monolayer WSe2–MoS2 lateral pn junction with an atomically sharp interface. Science 349, 524–528 (2015).

    ADS  Google Scholar 

  83. Hsu, W.-T. et al. Evidence of indirect gap in monolayer WSe2. Nat. Commun. 8, 929 (2017).

    ADS  Google Scholar 

  84. Hsu, W.-T. et al. Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers. Nat. Commun. 9, 1356 (2018).

    ADS  Google Scholar 

  85. Hsu, W.-T. et al. Tailoring excitonic states of van der Waals bilayers through stacking configuration, band alignment, and valley spin. Sci. Adv. 5, eaax7407 (2019).

    ADS  Google Scholar 

  86. Raja, A. et al. Dielectric disorder in two-dimensional materials. Nat. Nanotechnol. 14, 832–837 (2019).

    ADS  Google Scholar 

  87. Lien, D.-H. et al. Engineering light outcoupling in 2D materials. Nano Lett. 15, 1356–1361 (2015).

    ADS  Google Scholar 

  88. Robert, C. et al. Optical spectroscopy of excited exciton states MoS2 monolayers in van der Waals heterostructures. Phys. Rev. Mater. 2, 011001 (2018).

    Google Scholar 

  89. Fang, H. et al. Control of the exciton radiative lifetime in van der Waals heterostructures. Phys. Rev. Lett. 123, 067401 (2019).

    ADS  Google Scholar 

  90. Castellanos-Gomez, A. et al. Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping. 2D Mater. 1, 011002 (2014).

    Google Scholar 

  91. Purdie, D. et al. Cleaning interfaces in layered materials heterostructures. Nat. Commun. 9, 5387 (2018).

    ADS  Google Scholar 

  92. Wang, Z., Zhao, L., Mak, K. F. & Shan, J. Probing the spin-polarized electronic band structure in monolayer transition metal dichalcogenides by optical spectroscopy. Nano Lett. 17, 740–746 (2017).

    ADS  Google Scholar 

  93. Zhou, Y. et al. Controlling excitons in an atomically thin membrane with a mirror. Phys. Rev. Lett. 124, 027401 (2020).

    ADS  Google Scholar 

  94. Courtade, E. et al. Charged excitons in monolayer WSe2: experiment and theory. Phys. Rev. B 96, 085302 (2017).

    ADS  Google Scholar 

  95. Bermudez, V. M. & McClure, D. S. Spectroscopic studies of the two-dimensional magnetic insulators chromium trichloride and chromium tribromide-I. J. Phys. Chem. Solids 40, 129–147 (1979).

    ADS  Google Scholar 

  96. Molina-Sánchez, A., Catarina, G., Sangalli, D. & Fernández-Rossier, J. Magneto-optical response of chromium trihalide monolayers: chemical trends. J. Mater. Chem. C 8, 8856–8863 (2020).

    Google Scholar 

  97. Karni, O. et al. Infrared interlayer exciton emission in MoS2/WSe2 heterostructures. Phys. Rev. Lett. 123, 247402 (2019).

    ADS  Google Scholar 

  98. Ling, X., Wang, H., Huang, S., Xia, F. & Dresselhaus, M. S. The renaissance of black phosphorus. Proc. Natl Acad. Sci. USA 112, 4523–4530 (2015).

    ADS  Google Scholar 

  99. Ansari, L. et al. Quantum confinement-induced semimetal-to-semiconductor evolution in large-area ultra-thin PtSe2 films grown at 400 °C. npj 2D Mater. Appl. 3, 33 (2019).

    Google Scholar 

  100. Cassabois, G., Valvin, P. & Gil, B. Hexagonal boron nitride is an indirect bandgap semiconductor. Nat. Photonics 10, 262–266 (2016).

    ADS  Google Scholar 

  101. Kharche, N. & Nayak, S. K. Quasiparticle band gap engineering of graphene and graphone on hexagonal boron nitride substrate. Nano Lett. 11, 5274–5278 (2011).

    ADS  Google Scholar 

  102. Ramasubramaniam, A., Naveh, D. & Towe, E. Tunable band gaps in bilayer graphene–BN heterostructures. Nano Lett. 11, 1070–1075 (2011).

    ADS  Google Scholar 

  103. Spence, D. E., Kean, P. N. & Sibbett, W. 60-fsec pulse generation from a self-mode-locked Ti: sapphire laser. Opt. Lett. 16, 42–44 (1991).

    ADS  Google Scholar 

  104. Alfano, R. R. The Supercontinuum Laser Source: The Ultimate White Light (Springer, 2016).

  105. Arora, A. et al. Interlayer excitons in a bulk van der Waals semiconductor. Nat. Commun. 8, 639 (2017).

    ADS  Google Scholar 

  106. Leisgang, N. et al. Giant Stark splitting of an exciton in bilayer MoS2. Nat. Nanotechnol. 15, 901–907 (2020).

    ADS  Google Scholar 

  107. Zhang, X.-X. et al. Magnetic brightening and control of dark excitons in monolayer WSe2. Nat. Nanotechnol. 12, 883–888 (2017).

    ADS  Google Scholar 

  108. Wang, G. et al. Control of exciton valley coherence in transition metal dichalcogenide monolayers. Phys. Rev. Lett. 117, 187401 (2016).

    ADS  Google Scholar 

  109. Goryca, M. et al. Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields. Nat. Commun. 10, 4172 (2019).

    ADS  Google Scholar 

  110. Klingshirn, C. F. Semiconductor Optics (Springer, 2012).

  111. 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).

    ADS  Google Scholar 

  112. Ho, C., Huang, Y., Tiong, K. & Liao, P. Absorption-edge anisotropy in ReS2 and ReSe2 layered semiconductors. Phys. Rev. B 58, 16130 (1998).

    ADS  Google Scholar 

  113. Zhang, E. et al. Tunable ambipolar polarization-sensitive photodetectors based on high-anisotropy ReSe2 nanosheets. ACS Nano 10, 8067–8077 (2016).

    Google Scholar 

  114. Horng, J. et al. Observation of interlayer excitons in MoSe2 single crystals. Phys. Rev. B 97, 241404 (2018).

    ADS  Google Scholar 

  115. Arora, A. et al. Valley-contrasting optics of interlayer excitons in Mo- and W-based bulk transition metal dichalcogenides. Nanoscale 10, 15571–15577 (2018).

    Google Scholar 

  116. Gerber, I. C. et al. Interlayer excitons in bilayer MoS2 with strong oscillator strength up to room temperature. Phys. Rev. B 99, 035443 (2019).

    ADS  Google Scholar 

  117. Slobodeniuk, A. et al. Fine structure of K-excitons in multilayers of transition metal dichalcogenides. 2D Mater. 6, 025026 (2019).

    Google Scholar 

  118. Lorchat, E. et al. Dipolar and magnetic properties of strongly absorbing hybrid interlayer excitons in pristine bilayer MoS2. Preprint at https://arxiv.org/abs/2004.12753 (2020).

  119. Pelant, I. & Valenta, J. Luminescence Spectroscopy of Semiconductors (Oxford Univ. Press, 2012).

  120. Haunschild, J. et al. Quality control of as-cut multicrystalline silicon wafers using photoluminescence imaging for solar cell production. Solar Energy Mater. Solar Cells 94, 2007–2012 (2010).

    Google Scholar 

  121. Balocchi, A., Amand, T. & Marie, X. in Semiconductor Research (eds Patane, A. & Balkan, N.) 223–258 (Springer, 2012).

  122. Jakubczyk, T. et al. Radiatively limited dephasing and exciton dynamics in MoSe2 monolayers revealed with four-wave mixing microscopy. Nano Lett. 16, 5333–5339 (2016).

    ADS  Google Scholar 

  123. Hao, K. et al. Coherent and incoherent coupling dynamics between neutral and charged excitons in monolayer MoSe2. Nano Lett. 16, 5109–5113 (2016).

    ADS  Google Scholar 

  124. Robert, C. et al. Fine structure and lifetime of dark excitons in transition metal dichalcogenide monolayers. Phys. Rev. B 96, 155423 (2017).

    ADS  Google Scholar 

  125. Shree, S. et al. Observation of exciton-phonon coupling in MoSe2 monolayers. Phys. Rev. B 98, 035302 (2018).

    ADS  Google Scholar 

  126. Nagler, P. et al. Zeeman splitting and inverted polarization of biexciton emission in monolayer WS2. Phys. Rev. Lett. 121, 057402 (2018).

    ADS  Google Scholar 

  127. Sun, D. et al. Observation of rapid exciton–exciton annihilation in monolayer molybdenum disulfide. Nano Lett. 14, 5625–5629 (2014).

    ADS  Google Scholar 

  128. Barbone, M. et al. Charge-tuneable biexciton complexes in monolayer WSe2. Nat. Commun. 9, 3721 (2018).

    ADS  Google Scholar 

  129. Paradisanos, I. et al. Room temperature observation of biexcitons in exfoliated WS2 monolayers. Appl. Phys. Lett. 110, 193102 (2017).

    ADS  Google Scholar 

  130. Sigl, L. et al. Condensation signatures of photogenerated interlayer excitons in a van der Waals heterostack. Preprint at https://arxiv.org/abs/2001.07567 (2020).

  131. Taniguchi, T. & Watanabe, K. Synthesis of high-purity boron nitride single crystals under high pressure by using Ba-BN solvent. J. Cryst. Growth 303, 525–529 (2007).

    Google Scholar 

  132. Zhu, C. et al. Strain tuning of optical emission energy and polarization in monolayer and bilayer MoS2. Phys. Rev. B 88, 121301 (2013).

    ADS  Google Scholar 

  133. Berger, S. et al. Optical properties of carbon nanotubes in a composite material: the role of dielectric screening and thermal expansion. J. Appl. Phys. 105, 094323 (2009).

    ADS  Google Scholar 

  134. Hirana, Y., Tanaka, Y., Niidome, Y. & Nakashima, N. Strong micro-dielectric environment effect on the band gaps of (n, m) single-walled carbon nanotubes. J. Am. Chem. Soc. 132, 13072–13077 (2010).

    Google Scholar 

  135. Ai, N., Walden-Newman, W., Song, Q., Kalliakos, S. & Strauf, S. Suppression of blinking and enhanced exciton emission from individual carbon nanotubes. ACS Nano 5, 2664–2670 (2011).

    Google Scholar 

  136. Noe, J. C. et al. Environmental electrometry with luminescent carbon nanotubes. Nano Lett. 18, 4136–4140 (2018).

    ADS  Google Scholar 

  137. Raynaud, C. et al. Superlocalization of excitons in carbon nanotubes at cryogenic temperature. Nano Lett. 19, 7210–7216 (2019).

    ADS  Google Scholar 

  138. Blancon, J.-C. et al. Scaling law for excitons in 2D perovskite quantum wells. Nat. Commun. 9, 1–10 (2018).

    Google Scholar 

  139. Zhang, H. et al. Interference effect on optical signals of monolayer MoS2. Appl. Phys. Lett. 107, 101904 (2015).

    ADS  Google Scholar 

  140. Roddaro, S., Pingue, P., Piazza, V., Pellegrini, V. & Beltram, F. The optical visibility of graphene: interference colors of ultrathin graphite on SiO2. Nano Lett. 7, 2707–2710 (2007).

    ADS  Google Scholar 

  141. Lagarde, D. et al. Carrier and polarization dynamics in monolayer MoS2. Phys. Rev. Lett. 112, 047401 (2014).

    ADS  Google Scholar 

  142. Robert, C. et al. Exciton radiative lifetime in transition metal dichalcogenide monolayers. Phys. Rev. B 93, 205423 (2016).

    ADS  Google Scholar 

  143. Bandurin, D. A. et al. High electron mobility, quantum Hall effect and anomalous optical response in atomically thin InSe. Nat. Nanotechnol. 12, 223 (2017).

    ADS  Google Scholar 

  144. Liu, E. et al. Multipath optical recombination of intervalley dark excitons and trions in monolayer WSe2. Phys. Rev. Lett. 124, 196802 (2020).

    ADS  Google Scholar 

  145. Luo, Y. et al. Exciton dipole orientation of strain-induced quantum emitters in WSe2. Nano Lett. 20, 5119–5126 (2020).

    ADS  Google Scholar 

  146. Lu, Z. et al. Magnetic field mixing and splitting of bright and dark excitons in monolayer MoSe2. 2D Mater. 7, 015017 (2019).

    Google Scholar 

  147. Rivera, P. et al. Interlayer valley excitons in heterobilayers of transition metal dichalcogenides. Nat. Nanotechnol. 13, 1004–1015 (2018).

    ADS  Google Scholar 

  148. Jauregui, L. A. et al. Electrical control of interlayer exciton dynamics in atomically thin heterostructures. Science 366, 870–875 (2019).

    ADS  Google Scholar 

  149. Mupparapu, R., Bucher, T. & Staude, I. Integration of two-dimensional transition metal dichalcogenides with Mie-resonant dielectric nanostructures. Adv. Phys. X 5, 1734083 (2020).

    Google Scholar 

  150. Vasista, A. B., Sharma, D. K. & Kumar, G. P. Fourier plane optical microscopy and spectroscopy. Digital Encyclopedia of Applied Physics https://doi.org/10.1002/3527600434.eap817 (2003).

    Article  Google Scholar 

  151. Vasista, A. B. et al. Differential wavevector distribution of surface-enhanced Raman scattering and fluorescence in a film-coupled plasmonic nanowire cavity. Nano Lett. 18, 650–655 (2018).

    ADS  Google Scholar 

  152. Gu, J., Chakraborty, B., Khatoniar, M. & Menon, V. M. A room-temperature polariton light-emitting diode based on monolayer WS2. Nat. Nanotechnol. 14, 1024–1028 (2019).

    ADS  Google Scholar 

  153. Wagner, R., Heerklotz, L., Kortenbruck, N. & Cichos, F. Back focal plane imaging spectroscopy of photonic crystals. Appl. Phys. Lett. 101, 081904 (2012).

    ADS  Google Scholar 

  154. Graf, A., Tropf, L., Zakharko, Y., Zaumseil, J. & Gather, M. C. Near-infrared exciton-polaritons in strongly coupled single-walled carbon nanotube microcavities. Nat. Commun. 7, 13078 (2016).

    ADS  Google Scholar 

  155. Yoshikawa, K., Matsuda, K. & Kanemitsu, Y. Exciton transport in suspended single carbon nanotubes studied by photoluminescence imaging spectroscopy. J. Phys. Chem. C 114, 4353–4356 (2010).

    Google Scholar 

  156. Cadiz, F. et al. Exciton diffusion in WSe2 monolayers embedded in a van der Waals heterostructure. Appl. Phys. Lett. 112, 152106 (2018).

    ADS  Google Scholar 

  157. Kulig, M. et al. Exciton diffusion and halo effects in monolayer semiconductors. Phys. Rev. Lett. 120, 207401 (2018).

    ADS  Google Scholar 

  158. Rivera, P. et al. Valley-polarized exciton dynamics in a 2D semiconductor heterostructure. Science 351, 688–691 (2016).

    ADS  Google Scholar 

  159. Unuchek, D. et al. Valley-polarized exciton currents in a van der Waals heterostructure. Nat. Nanotechnol. 14, 1104–1109 (2019).

    ADS  Google Scholar 

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

    ADS  Google Scholar 

  161. Ciarrocchi, A. et al. Polarization switching and electrical control of interlayer excitons in two-dimensional van der Waals heterostructures. Nat. Photonics 13, 131–136 (2019).

    ADS  Google Scholar 

  162. Hill, H. M. et al. Observation of excitonic Rydberg states in monolayer MoS2 and WS2 by photoluminescence excitation spectroscopy. Nano Lett. 15, 2992–2997 (2015).

    ADS  Google Scholar 

  163. Srivastava, A. & Imamoğlu, A. Signatures of Bloch-band geometry on excitons: nonhydrogenic spectra in transition-metal dichalcogenides. Phys. Rev. Lett. 115, 166802 (2015).

    ADS  Google Scholar 

  164. Glazov, M. et al. Intrinsic exciton-state mixing and nonlinear optical properties in transition metal dichalcogenide monolayers. Phys. Rev. B 95, 035311 (2017).

    ADS  Google Scholar 

  165. Berghäuser, G., Knorr, A. & Malic, E. Optical fingerprint of dark 2p-states in transition metal dichalcogenides. 2D Mater. 4, 015029 (2016).

    Google Scholar 

  166. Wang, G. et al. Exciton states in monolayer MoSe2: impact on interband transitions. 2D Mater. 2, 045005 (2015).

    Google Scholar 

  167. Chow, C. M. et al. Phonon-assisted oscillatory exciton dynamics in monolayer MoSe2. npj 2D Mater. Appl. 1, 33 (2017).

    ADS  Google Scholar 

  168. Soubelet, P. et al. Resonance effects in the Raman scattering of monolayer and few-layer MoSe2. Phys. Rev. B 93, 155407 (2016).

    ADS  Google Scholar 

  169. Kioseoglou, G. et al. Valley polarization and intervalley scattering in monolayer MoS2. Appl. Phys. Lett. 101, 221907 (2012).

    ADS  Google Scholar 

  170. Tornatzky, H., Kaulitz, A.-M. & Maultzsch, J. Resonance profiles of valley polarization in single-layer MoS2 and MoSe2. Phys. Rev. Lett. 121, 167401 (2018).

    ADS  Google Scholar 

  171. Dufferwiel, S. et al. Valley-addressable polaritons in atomically thin semiconductors. Nat. Photonics 11, 497–501 (2017).

    Google Scholar 

  172. Dufferwiel, S. et al. Valley coherent exciton-polaritons in a monolayer semiconductor. Nat. Commun. 9, 4797 (2018).

    ADS  Google Scholar 

  173. Paradisanos, I. et al. Prominent room temperature valley polarization in WS2/graphene heterostructures grown by chemical vapor deposition. Appl. Phys. Lett. 116, 203102 (2020).

    ADS  Google Scholar 

  174. Rosenberger, M. R. et al. Twist angle-dependent atomic reconstruction and moiré patterns in transition metal dichalcogenide heterostructures. ACS Nano 14, 4550–4558 (2020).

    Google Scholar 

  175. Yu, H., Liu, G.-B. & Yao, W. Brightened spin-triplet interlayer excitons and optical selection rules in van der Waals heterobilayers. 2D Mater. 5, 035021 (2018).

    Google Scholar 

  176. Molas, M. et al. Probing and manipulating valley coherence of dark excitons in monolayer WSe2. Phys. Rev. Lett. 123, 096803 (2019).

    ADS  Google Scholar 

  177. Srivastava, A. et al. Valley Zeeman effect in elementary optical excitations of monolayer WSe2. Nat. Phys. 11, 141–147 (2015).

    Google Scholar 

  178. Nagler, P. et al. Giant magnetic splitting inducing near-unity valley polarization in van der Waals heterostructures. Nat. Commun. 8, 1551 (2017).

    ADS  Google Scholar 

  179. Back, P. Giant magnetic splitting inducing near-unity valley polarization in van der Waals heterostructures. Phys. Rev. Lett. 118, 237404 (2017).

    ADS  Google Scholar 

  180. Carvalho, B. R., Malard, L. M., Alves, J. M., Fantini, C. & Pimenta, M. A. Symmetry-dependent exciton-phonon coupling in 2D and bulk MoS2 observed by resonance Raman scattering. Phys. Rev. Lett. 114, 136403 (2015).

    ADS  MathSciNet  Google Scholar 

  181. Scheuschner, N., Gillen, R., Staiger, M. & Maultzsch, J. Interlayer resonant Raman modes in few-layer MoS2. Phys. Rev. B 91, 235409 (2015).

    ADS  Google Scholar 

  182. Oliver, S. M. et al. The structural phases and vibrational properties of Mo1−xWxTe2 alloys. 2D Mater. 4, 045008 (2017).

    Google Scholar 

  183. Wolverson, D., Crampin, S., Kazemi, A. S., Ilie, A. & Bending, S. J. Raman spectra of monolayer, few-layer, and bulk ReSe2: an anisotropic layered semiconductor. ACS Nano 8, 11154–11164 (2014).

    Google Scholar 

  184. Chakraborty, B. et al. Symmetry-dependent phonon renormalization in monolayer MoS2 transistor. Phys. Rev. B 85, 161403 (2012).

    ADS  Google Scholar 

  185. Bertolazzi, S. et al. Engineering chemically active defects in monolayer MoS2 transistors via ion-beam irradiation and their healing via vapor deposition of alkanethiols. Adv. Mater. 29, 1606760 (2017).

    Google Scholar 

  186. Conley, H. J. et al. Bandgap engineering of strained monolayer and bilayer MoS2. Nano Lett. 13, 3626–3630 (2013).

    ADS  Google Scholar 

  187. Mignuzzi, S. et al. Effect of disorder on Raman scattering of single-layer MoS2. Phys. Rev. B 91, 195411 (2015).

    ADS  Google Scholar 

  188. Buscema, M., Steele, G. A., van der Zant, H. S. & Castellanos-Gomez, A. The effect of the substrate on the Raman and photoluminescence emission of single-layer MoS2. Nano Res. 7, 561–571 (2014).

    Google Scholar 

  189. Lee, C. et al. Anomalous lattice vibrations of single- and few-layer MoS2. ACS Nano 4, 2695–2700 (2010).

    Google Scholar 

  190. Zhang, X. et al. Raman spectroscopy of shear and layer breathing modes in multilayer MoS2. Phys. Rev. B 87, 115413 (2013).

    ADS  Google Scholar 

  191. Debnath, R. et al. Evolution of high-frequency Raman modes and their doping dependence in twisted bilayer MoS2. Nanoscale 12, 17272–17280 (2020).

    Google Scholar 

  192. Hsu, W.-T. et al. Second harmonic generation from artificially stacked transition metal dichalcogenide twisted bilayers. ACS Nano 8, 2951–2958 (2014).

    Google Scholar 

  193. Shinde, S. M. et al. Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2. NPG Asia Mater. 10, e468 (2018).

    Google Scholar 

  194. Psilodimitrakopoulos, S. et al. Twist angle mapping in layered WS2 by polarization-resolved second harmonic generation. Sci. Rep. 9, 14285–11 (2019).

    ADS  Google Scholar 

  195. Psilodimitrakopoulos, S. et al. Ultrahigh-resolution nonlinear optical imaging of the armchair orientation in 2D transition metal dichalcogenides. Light Sci. Appl. 7, 18005 (2018).

    ADS  Google Scholar 

  196. Mennel, L., Paur, M. & Mueller, T. Second harmonic generation in strained transition metal dichalcogenide monolayers: MoS2, MoSe2, WS2, and WSe2. APL Photonics 4, 034404 (2019).

    Google Scholar 

  197. Farenbruch, A. et al. Magneto-Stark and Zeeman effect as origin of second harmonic generation of excitons in Cu2O. Phys. Rev. B 101, 115201 (2020).

    ADS  Google Scholar 

  198. Seyler, K. L. et al. Electrical control of second-harmonic generation in a WSe2 monolayer transistor. Nat. Nanotechnol. 10, 407–411 (2015).

    ADS  Google Scholar 

  199. Kaminski, B. et al. Spin-induced optical second harmonic generation in the centrosymmetric magnetic semiconductors EuTe and EuSe. Phys. Rev. Lett. 103, 057203 (2009).

    ADS  Google Scholar 

  200. Sun, Z. et al. Topographic and electronic contrast of the graphene moiré on Ir(111) probed by scanning tunneling microscopy and noncontact atomic force microscopy. Phys. Rev. B 83, 081415 (2011).

    ADS  Google Scholar 

  201. de la Torre, B. et al. Atomic-scale variations of the mechanical response of 2D materials detected by noncontact atomic force microscopy. Phys. Rev. Lett. 116, 245502 (2016).

    ADS  Google Scholar 

  202. Darlington, T. P. et al. Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room temperature. Nat. Nanotechnol. 15, 854–860 (2020).

    ADS  Google Scholar 

  203. Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nat. Commun. 3, 887 (2012).

    ADS  Google Scholar 

  204. Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nat. Nanotechnol. 7, 494–498 (2012).

    ADS  Google Scholar 

  205. Sallen, G. et al. Robust optical emission polarization in MoS2 monolayers through selective valley excitation. Phys. Rev. B 86, 081301 (2012).

    ADS  Google Scholar 

  206. Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nat. Nanotechnol. 7, 490–493 (2012).

    ADS  Google Scholar 

  207. Unuchek, D. Spin–Valley Optoelectronics Based on Two-dimensional Materials. Thesis, EPFL (2019).

  208. Hecht, E. et al. Optics Vol. 4 (Addison Wesley, 2002).

  209. Pawley, J. Handbook of Biological Confocal Microscopy Vol. 236 (Springer, 2006).

  210. Kuhlmann, A. V. et al. A dark-field microscope for background-free detection of resonance fluorescence from single semiconductor quantum dots operating in a set-and-forget mode. Rev. Sci. Instrum. 84, 073905 (2013).

    ADS  Google Scholar 

  211. Benelajla, M., Kammann, E., Urbaszek, B. & Karrai, K. The physical origins of extreme cross-polarization extinction in confocal microscopy. Preprint at https://arxiv.org/abs/2004.13564 (2020).

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Acknowledgements

The authors acknowledge funding from ANR 2D-vdW-Spin, ANR VallEx, ANR MagicValley, ITN 4PHOTON Marie Sklodowska Curie Grant Agreement no. 721394 and the Institut Universitaire de France. The authors thank H. Tornatzky, D. Lagarde, A. Balocchi, N. Leisgang, H. Park and M. Glazov for discussions, and Y. Zhou for providing data from Zhou et al. Phys. Rev. Lett. 124, 027401 (2020).

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  1. Université de Toulouse, INSA-CNRS-UPS, LPCNO, Toulouse, France

    Shivangi Shree, Ioannis Paradisanos, Xavier Marie, Cedric Robert & Bernhard Urbaszek

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All authors contributed to the discussion of content and researched data for the article. S.S., I.P. and C.R. wrote the manuscript with critical input from X.M. and B.U.

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Glossary

Multilayers

Structures consisting of more than one layer.

Excitons

Coulomb-bound electron–hole pairs.

Bright and dark optical transitions

A spin- and dipole-allowed transition is ‘bright’ whereas a spin- and/or dipole-forbidden transition is ‘dark’.

Heterobilayers

Lateral or vertical heterojunctions formed by combining two different monolayers.

Moiré effects

Effects related to the interference pattern produced by the superposition of two slightly different lattice constants and/or twist angles.

Reconstructions

Spontaneous translational or angular rearrangements of atoms within multilayers, aiming for a lattice configuration with the lowest energy.

M 2 factor

Represents the degree of variation of a beam from an ideal Gaussian beam. This factor reflects how well a collimated laser beam can be focused to a small spot, or how well a divergent laser source can be collimated.

Quasiparticle bandgap

Bandgap of free electrons and holes; the exciton resonance energies lie in energy below the quasiparticle bandgap.

Homobilayers and homotrilayers

Stacking of two and three monolayers of the same material, respectively.

Four-wave mixing

Nonlinear effect arising from the third-order optical nonlinearity where one or two new wavelengths are produced by interactions between two or three wavelengths. Four-wave-mixing microspectroscopy accesses coherence and population dynamics of excitons.

Two-colour pump–probe experiments

Pump–probe experiments using two distinct laser beams where the wavelengths of the pump and probe beams are not identical.

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Shree, S., Paradisanos, I., Marie, X. et al. Guide to optical spectroscopy of layered semiconductors. Nat Rev Phys 3, 39–54 (2021). https://doi.org/10.1038/s42254-020-00259-1

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