Conformational control of exciton-polariton physics in metal-poly(9,9-dioctylfluorene)-metal cavities

F. Le Roux and D. D. C. Bradley
Phys. Rev. B 98, 195306 – Published 15 November 2018
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Abstract

Control is exerted over the exciton-polariton physics in metal-poly(9,9-dioctylfluorene)-metal microcavities via conformational changes to the polymer backbone. Using thin-film samples containing increasing fractions of β-phase chain segments, a systematic study is reported for the mode characteristics and resulting light emission properties of cavities containing two distinct exciton subpopulations within the same semiconductor. Ultrastrong coupling for disordered glassy-phase excitons is observed from angle-resolved reflectivity measurements, with Rabi splitting energies in excess of 1.05 eV (more than 30% of the exciton transition energy) for both TE- and TM-polarized light. A splitting of the lower polariton branch is then induced via introduction of β-phase excitons and increases with their growing fraction. In all cases, the photoluminescence emanates from the lowermost polariton branch, allowing conformational control to be exerted over the emission energy and its angular variation. Dispersion-free cavities with highly saturated blue-violet emission are thus enabled. Experimental results are discussed in terms of the full Hopfield Hamiltonian generalized to the case of two exciton oscillators. The importance of taking account of the molecular characteristics of the semiconductor for an accurate description of its strong coupling behavior is directly considered, in specific relation to the role of the vibronic structure.

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  • Received 6 September 2018
  • Revised 23 October 2018

DOI:https://doi.org/10.1103/PhysRevB.98.195306

©2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

F. Le Roux

  • Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom

D. D. C. Bradley

  • Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom and Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, United Kingdom

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Issue

Vol. 98, Iss. 19 — 15 November 2018

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