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Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites

An Author Correction to this article was published on 14 February 2019

This article has been updated


Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (50 cm−1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.

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Fig. 1: Impulsive coherent vibrational dynamics of (PEA)2PbI4.
Fig. 2: Integrated resonant impulsive stimulated Raman spectrum of (PEA)2PbI4 and (NBT)2PbI4 at 5 K and associated phonon modes.
Fig. 3: Pump wavelength dependence of the resonant impulsive stimulated Raman spectra of (PEA)2PbI4 at 5 K.
Fig. 4: Consequences of the wavepacket dynamics in (PEA)2PbI4 at 5 K.

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The experimental data and analysis material that support the findings of this study are available in the Scholarly Materials And Research @ Georgia Tech repository (SMARTech),

Change history

  • 14 February 2019

    In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV. They should have been eV. This has now been corrected in all versions of the Article.


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A.R.S.K. acknowledges funding from EU Horizon 2020 via a Marie Sklodowska Curie Fellowship (Global) (project no. 705874). F.T. acknowledges support from a doctoral postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada and Fond Québécois pour la Recherche: Nature et Technologies. This work is partially supported by the National Science Foundation (award 1838276). C.S. acknowledges support from the School of Chemistry and Biochemistry and the College of Science of Georgia Institute of Technology. The work at Mons was supported by the Interuniversity Attraction Pole programme of the Belgian Federal Science Policy Office (PAI 6/27) and FNRS-F.R.S. Computational resources have been provided by the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under grant no. 2.5020.11. D.B. is an FNRS Research Director.

Author information

Authors and Affiliations



F.T., D.A.V.-C., I.B. and A.R.S.K. carried out transient absorption measurements. F.T. and D.A.V.-C. performed the analysis of the experimental data. C.Q. performed ab initio calculations. D.C. synthesized the samples. A.P. supervised the sample preparation activity, D.B. supervised the ab initio calculations, and C.S. and A.R.S.K. supervised the ultrafast spectroscopy activity. A.R.S.K. and C.S. conceived the project. All authors contributed to the redaction of the manuscript. F.T. and D.A.V.-C. are to be considered first co-authors, and C.S. and A.R.S.K. corresponding co-authors.

Corresponding authors

Correspondence to Carlos Silva or Ajay Ram Srimath Kandada.

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Supplementary information

Supplementary Information

Supplementary Sections 1–5, Supplementary Figures 1–17, Supplementary Tables 1–2, Supplementary References 1–3

NBT Normal Mode N1

Video of normal mode N1 for (NBT)2PbI4 reported in Table I

NBT Normal Mode N2

Video of normal mode N2 for (NBT)2PbI4 reported in Table I

NBT Normal Mode N3

Video of normal mode N3 for (NBT)2PbI4 reported in Table I

NBT Normal Mode N4

Video of normal mode N4 for (NBT)2PbI4 reported in Table I

NBT Normal Mode N5

Video of normal mode N5 for (NBT)2PbI4 reported in Table I

PEA Normal Mode M1

Video of normal mode M1 for (PEA)2PbI4 reported in Table I

PEA Normal Mode M2

Video of normal mode M2 for (PEA)2PbI4 reported in Table I

PEA Normal Mode M3

Video of normal mode M3 for (PEA)2PbI4 reported in Table I

PEA Normal Mode M4

Video of normal mode M4 for (PEA)2PbI4 reported in Table I

PEA Normal Mode M5

Video of normal mode M5 for (PEA)2PbI4 reported in Table I

PEA Normal Mode M6

Video of normal mode M6 for (PEA)2PbI4 reported in Table I

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Thouin, F., Valverde-Chávez, D.A., Quarti, C. et al. Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites. Nat. Mater. 18, 349–356 (2019).

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