Conformational Control of Exciton-Polariton Physics in Metal - Poly(9,9-dioctylfluorene) - Metal Cavities

TL;DR

This study demonstrates how conformational changes in polymer backbones within metal microcavities can control exciton-polariton interactions, enabling tunable emission properties and ultrastrong coupling with potential applications in advanced photonic devices.

Contribution

It introduces a systematic approach to modulate exciton-polariton physics through polymer conformational control in metal cavities, including the observation of ultrastrong coupling with Rabi splitting over 1.05 eV.

Findings

Ultrastrong coupling observed with Rabi splitting >1.05 eV

Conformational control enables tuning of emission energy and angular properties

Dispersion-free cavities with saturated blue-violet emission achieved

Abstract

Control is exerted over the exciton-polariton physics in metal - Poly(9,9-dioctyl fluorene) - metal microcavities via conformational changes to the polymer backbone. Using thin-film samples containing increasing fractions of $\beta$-phase chain segments, a systematic study is reported for the mode characteristics and resulting light emission properties of cavities containing two distinct exciton sub-populations 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 $\beta$-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 behaviour is directly considered, in specific relation to the role of the vibronic structure.