Magnetic-field-induced cavity polariton linewidth reduction in aGaAs/Al0.1Ga0.9Asmicrocavity

Abstract

The magnetic-field $(Bl~7\mathrm{T})$ effect on the cavity polaritons linewidth is studied by reflection spectroscopy at $T=2--5\mathrm{K}.$ The structure under study consists of a single 160-\AA{} GaAs/AlAs quantum well (QW) embedded in a \ensuremath{\lambda}-wide ${\mathrm{Al}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}$ microcavity (MC) that is cladded by ${\mathrm{Al}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}\mathrm{A}\mathrm{s}$ distributed Bragg reflectors. The QW absorption above the QW band gap, $EgE(e1\ensuremath{-}\mathrm{hh}1),$ is flat and it transforms into a series of well-defined bands (Landau transitions or magnetoexcitons) under a perpendicularly applied magnetic field. This results in a narrowing of the MC mode by about 30% when ${E}_{\mathrm{MC}}gE(e1\ensuremath{-}\mathrm{hh}1).$ We analyze the reflection spectra by using the linear dispersion model based on the transfer-matrix formalism and introducing the $(e1:\mathrm{hh}1)1S,$ $(e1:\mathrm{lh}1)1S$ excitons and the $N=1$ and $N=2$ interband Landau transitions as Lorentzian oscillators. The model explains well the reduction in the MC mode linewidth, under the applied magnetic field, as due to the change in the absorption spectrum caused by the transformation from a two- to zero-dimensional electronic density of states. It is also found that the MC mode linewidth and intensity, in the spectral range ${E}_{\mathrm{MC}}lE(e1:\mathrm{hh}1)1S,$ are strongly affected by below-band-gap residual absorption of the ${\mathrm{Al}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}$ layers.