Fifteen Years of Microcavity Polaritons

Abstract

In semiconductors with a direct interband optical transition, the fundamental electronic excitations above the ground state are excitons, namely hydrogen-like bound electron-hole pairs. In a perfect bulk semiconductor material, however, a correct description of the excited states must include the linear coupling of excitons to the electromagnetic field. This coupling gives rise to normal modes that are linear superpositions of one exciton and one photon mode, called exciton-polaritons . Exciton-polaritons are the actual excited states of a bulk semiconductor.Bulk polaritons were suggested in 1958 by J. Hopfield [58] and measured a few years later by means of non-linear optical spectroscopy [2,52,57,152]. The normal-mode coupling for polaritons is aresult of momentum conservation in the exciton-photon interaction. This selection rule imposes a one-to-one coupling between exciton and photon modes having the same momentum. As a consequence, within the linear coupling regime, the situation is analogous to that of two linearlycoupled harmonic oscillators. Two normal modes at different energies, the upper and the lower polariton, are formed. Due to the very different exciton and photon energy dispersion, as a function of momentum, polariton modes display an anticrossing with a minimum energy separation that can be as large as 16 meV in bulk GaAs [2]. Within the anticrossing region, polaritons are full admixtures of exciton and photon modes, while they have pure exciton or photon character far from it.The concept of polaritons remained linked to the physics of bulk semiconductors for more than two decades. The progress in fabrication of epitaxial semiconductor heterostructures, particularly quantum wells (QWs) led naturally to a description of their electronic excitations in terms of the polariton concept. However, because of the mismatch in the dimensionality of excitons (2D) and photons (3D), momentum conservation applies only to the in-plane component, and one exciton mode couples to a continuum of photon modes, resulting in an irreversible radiative decay instead of a normal-mode coupling [6,44]. Only at larger in-plane momenta, photon modes that are evanescent in the direction orthogonal to the QW can form surface polari- Physics of Semiconductor Microcavities: From Fundamentals toNanoscale DevicesEdited by Benoit Deveaud

Room-Temperature Strong Coupling between CdSe Nanoplatelets and a Metal–DBR Fabry–Pérot Cavity

“…Thus, including momentum-related dispersion, strong light-matter coupling produces an upper polariton (UP) and a lower polariton (LP) branch, which have a relative admixture of excitonic and photonic properties. 37,38 According to the Tavis-Cummings model, 39 the eigenenergies corresponding to UP (E + ) and LP (E − ) under the collective light-matter coupling regime can be expressed as…”

Room-Temperature Strong Coupling between CdSe Nanoplatelets and a Metal–DBR Fabry–Pérot Cavity

“…Thus, including momentum-related dispersion, strong light-matter coupling produces an upper polariton (UP) and a lower polariton (LP) branch, which have a relative admixture of excitonic and photonic properties. 37,38 According to the Tavis-Cummings model, 39 the eigenenergies corresponding to UP (E + ) and LP (E − ) under the collective light-matter coupling regime can be expressed as…”

Room-Temperature Strong Coupling between CdSe Nanoplatelets and a Metal-DBR Fabry–Pérot Cavity

“…Strong coupling is thus characterized by an avoided crossing between the coupled modes and the emergence of two equal-intensity transition peaks at resonance separated by this Rabi splitting 45 . These new eigenmodes resulting from the quantum superposition of excitons and cavity photons, known as the upper polariton (UP) and lower polariton (LP) branches, exhibit a complete admixture of excitonic and photonic properties in the strong coupling regime 46,47 . The energies corresponding to the LP and UP branches can be expressed as…”