Fate of the upper polariton: Breakdown of the quasiparticle picture in the continuum br

Organic polaritons, strongly hybridized light-matter excitations, have arisen as a platform to device opticalinterfaces at room temperature. Despite their inherent complexity, polaritons are commonly regarded as coherentexcitations described by Landau's quasiparticle theory. Here, we theoretically study and experimentally demon-strate the role of incoherent matter excitations in terms of generalized Hopfield coefficients, which unveil thefading of the upper polariton at its entrance to a continuum of molecular excitations. This marks the breakdownof the simplistic quasiparticle picture and the formation of a more complex quantum state beyond Landau's formalism.

Automated summary

Organic polaritons, which are hybridized light-matter excitations, can be used as a platform for optical interfaces at room temperature. Previous studies have described polaritons as coherent excitations according to Landau's quasiparticle theory. However, this study reveals the role of incoherent matter excitations and demonstrates the breakdown of the quasiparticle picture at the entrance of upper polaritons into a continuum of molecular excitations. This leads to the formation of a more complex quantum state beyond Landau's formalism.