Evidence of polariton-induced transparency in a single organic quantum wire

Abstract

The resonant interaction between quasi-one dimensional excitons and photons is investigated. For a single isolated organic quantum wire, embedded in its single crystal monomer matrix, the strong exciton-photon coupling regime is reached. This is evidenced by the suppression of the resonant excitonic absorption arising when the system eigenstate is a polariton. These observations demonstrate that the resonant excitonic absorption in a semiconductor can be understood in terms of a balance between the exciton coherence time and the Rabi period between exciton-like and photon-like states of the polariton.In the 50's Hopfield showed that semiclassical theory is inappropriate to describe photon absorption by a semiconductor [1]. Indeed, an exciton has a defined wave-vector and is then only coupled to a single photon state, the one having the same momentum. The resulting system eigenstate during photoexcitation is a mixed exciton-photon state, a polariton, which does not lead to photon absorption if additional couplings are not taken into account [1].On the other hand, an exciton in a quantum well or wire is coupled to a photon continuum in the emission process. Therefore, the emission probability follows the Fermi Golden rule (FGR), whereas this is not a priori so for the absorption. In fact, as recently shown [2], two regimes can be reached by photoexcitation depending on the number of incident photons: a linear regime where photons are absorbed and a non linear one where absorption does not occur, the semiconductor becoming transparent. In the former, the exciton coherence time (generally governed by interaction with phonons) is much shorter than the exciton-photon interaction time [2], and photons are continuously absorbed following the FGR. In the latter, the system eigenstate is a slightly damped polariton, the exciton-photon interaction time

Vibronic coupling in quantum wires: Applications to polydiacetylene

“…(26) gives a thermal coherence length, (N coh − 1)d ≈ 350 Å, in excellent agreement with the coherence length (in blue-phase PDA) measured using the Franz-Keldysh effect in Ref. The coupling between the very large oscillator strength of the PDA chain and the light field may produce polaritons 34,35 at sufficiently large excitation light intensities. The value is, however, significantly less than the coherence length of several microns measured in microfluorescence experiments on red-phase PDA.…”

Stark effect and Franz-Keldysh effect of a quantum wire realized by conjugated polymer chains of a diacetylene 3NPh2

“…11,12 Coherent coupling of excitons on a single chain to a propagating laser …eld was veri…ed by micro‡uorescence 13 and by spatially coherent emission of a single chain. 14,15 By increasing the density of blue chains coherent coupling of excitons to radiation modes of the monomer crystal leads to a tightly bound polariton which enables transmission of light in resonance to the exciton through thick crystals of 3BCMU.…”

Structural study of two reactive diacetylenes

“…The conditions to obtain isolated chains behaving as perfect quantum wires [1,[6][7][8][9][10][11][12][13][14][15][16][17][18] are met in the reactive DA known as 3 and 4 BCMU which are studied in the present work. Their side-group formulae are R = R 0 = -(CH 2 ) n -OCONH-CH 2 -COOC 4 H 9 with n = 3 or 4 for 3BCMU and 4BCMU, respectively.…”