Zeeman splitting and diamagnetic shift of spatially confined quantum-well exciton polaritons in an external magnetic field

We report on pronounced magneto-optical effects of spatially confined polariton modes in an InGaAs quantum-well microcavity. The polaritons were trapped by a lithographically modulated cavity length. In contrast to etched structures suffering from nonradiative recombination, this approach allows for a gentle modification of the dielectric properties and results in a confinement potential of 7.5 meV. In the presence of an external magnetic field, a diamagnetic shift and Zeeman splitting of the quantized modes were observed for different trap diameters, ranging from 1 to 10 mu m. This confirms that the polaritonic properties of the emission modes are preserved even for small traps. Moreover, a clear correlation between the magnetic response and the excitonic fraction of the polaritons was identified by magnetic field-dependent measurements.