Investigating the Onset of the Strong Coupling Regime by Fine‐Tuning the Rabi Splitting in Multilayer Organic Microcavities

Abstract

Given the prevalence of disorder in many organic semiconductors, the applicability of simple models to describe their behavior in the strong coupling regime, such as the two‐level coupled oscillator, is not evident. Here, the validity of the two‐level coupled oscillator model and the simple dependence of the coupling strength on the number of absorbers and the electric field is tested experimentally in metal‐clad microcavities containing a disordered film of small molecules. Multilayer microcavities are produced by combining different thin film deposition techniques. These allow for isolating the relevant parameters and thus to confirm the coupling strength is proportional to 1) the square root of the number of absorbers and 2) the amplitude of the electric field. By changing either of these two parameters, the microcavities are shifted from the weak to the strong coupling regime. Moreover, careful analysis reveals that there is a threshold coupling strength for the onset of the Rabi splitting. Two independent investigations show that this threshold is comparable to the losses in the cavities. These results validate the coupled two‐level Hamiltonian for microcavities containing disordered organic semiconductors, even though the assumption of a single exciton level represents a strong simplification for these systems.

Strong Coupling beyond the Light-Line

“…One way to explore this is to make use of a coupled oscillators model to look at the contribution the different cavity modes and the molecular resonance make to the polaritons. This is a well-known approach 25 , 72 that we now adopt to look at a cavity close to the usual cutoff, that is, the situation shown in Figure 1 h. We chose this particular situation since a cavity close to cutoff is the commonly used system in many strong coupling experiments. As a first step we represent the dispersion of the TM 0 and TM –1 modes analytically, see Methods .…”

Enhanced and Polarization-Dependent Coupling for Photoaligned Liquid Crystalline Conjugated Polymer Microcavities

“…16,17 Experimental realizations of increasingly higher coupling ratios have also been reported for inorganic semiconductor based intersubband polaritons, 18 and other physical systems, including superconducting circuits, 19 Landau polaritons 20 and plasmonic picocavities interacting with vibrational degrees of freedom of individual molecules. 21 For an ensemble of Frenkel excitons inside a cavity for which both inhomogeneous (nonradiative broadening) and homogeneous broadening (radiative broadening and cavity damping) are small compared with the observed Ω R : [22][23][24]…”

“…For an ensemble of Frenkel excitons inside a cavity for which both inhomogeneous (nonradiative broadening) and homogeneous broadening (radiative broadening and cavity damping) are small compared with the observed ℏ Ω R , − where μ is the transition dipole moment, E the electric field, N the number of molecules, ℏ ω ex the exciton transition energy, ϵ eff the cavity effective permittivity, and V m the cavity mode volume.…”

Metamaterial Analogues of Strongly Coupled Molecular Ensembles

“…The cavities used in strong coupling experiments in the visible and infrared parts of the spectrum frequently make use of mirrors based on simple metal films. ,− These metal films are typically 30 nm or so thick, a thickness comparable with the skin depth. At this thickness, they are highly reflecting but still provide some degree of field penetration, allowing the incident light to be coupled in to the modes of the cavity.…”