Microcavity-like exciton-polaritons can be the primary photoexcitation in bare organic semiconductors

Abstract

Strong-coupling between excitons and confined photonic modes can lead to the formation of new quasi-particles termed exciton-polaritons which can display a range of interesting properties such as super-fluidity, ultrafast transport and Bose-Einstein condensation. Strong-coupling typically occurs when an excitonic material is confided in a dielectric or plasmonic microcavity. Here, we show polaritons can form at room temperature in a range of chemically diverse, organic semiconductor thin films, despite the absence of an external cavity. We find evidence of strong light-matter coupling via angle-dependent peak splittings in the reflectivity spectra of the materials and emission from collective polariton states. We additionally show exciton-polaritons are the primary photoexcitation in these organic materials by directly imaging their ultrafast (5 × 106 m s−1), ultralong (~270 nm) transport. These results open-up new fundamental physics and could enable a new generation of organic optoelectronic and light harvesting devices based on cavity-free exciton-polaritons

Tuning the Coherent Propagation of Organic Exciton‐Polaritons through Dark State Delocalization

“…We exploit these spectral signatures and the dynamical insights of our Q‐ factor dependence to interrogate the nature of polariton transport in the initial coherent regime using transient absorption microscopy (fs‐TAM). [ 58 , 59 , 60 ] In this technique, a pump pulse focused to the diffraction limit ( σ ≈ 140 nm on SiO 2 ) locally excites a region of the sample. A wide‐field counter‐propagating probe pulse then reads out the spatial pump‐probe signal generated, as a function of time.…”

Controlling Exciton Propagation in Organic Crystals through Strong Coupling to Plasmonic Nanoparticle Arrays

“…11 Later, long-range exciton polariton propagation was also experimentally demonstrated for organic media where excitons were coupled to Bloch surface waves 12,13 and for plasmonic nanoparticle arrays coupled to excitons in carbon nanotubes. 14 A much smaller enhancement of the transport length was achieved for Frenkel excitons strongly coupled to confined light modes of an optical microcavity 15 and for polaritons in cavity-free systems, 16 where the polaritons transport mechanism appeared to be (partially) diffusive. The reason for the different behavior of polaritons is not clear as a description of the underlying processes on the molecular/excitonic level is missing, leaving the polariton-enhanced transport mechanism open for interpretation.…”

Effect of Photonic Cavity Interactions on Femtosecond Multiphoton Optical Nonlinear Absorptions from Bi2O3-Based One-Dimensional Photonic Crystal

“…The photonic cavity-mediated enhanced optical nonlinearity has become the frontier research area in optics, photonics, and condensed matter physics. − In the wake of the advancement of ultrafast laser systems, the unprecedented light confinement in wavelength-order (volume ∼ (λ/2 n ) 3 ) photonic architectures results in significant third-order nonlinear optical processes (χ (3) ), leading to a myriad applications in the field of the optical waveguides, ultrafast pulse generation, and optical limiters. − Several approaches have been implemented to harness the enhanced nonlinearity utilizing the ultrafast χ (3) of nonlinear media sandwiched in various microcavities in strong and weak coupling regimes, which play a pivotal role in ultrafast optics and quantum information processing. − …”