Polaritonic Feshbach resonance

A Feshbach resonance occurs when the energy of two interacting free particles comes into resonance with a molecular bound state. When approaching this resonance, marked changes in the interaction strength between the particles can arise. Feshbach resonances provide a powerful tool for controlling the interactions in ultracold atomic gases, which can be switched from repulsive to attractive and have allowed a range of many-body quantum physics effects to be explored. Here we demonstrate a Feshbach resonance based on the polariton spinor interactions in a semiconductor microcavity. By tuning the energy of two polaritons with anti-parallel spins across the biexciton bound state energy, we show an enhancement of attractive interactions and a prompt change to repulsive interactions. A mean-field two-channel model quantitatively reproduces the experimental results. This observation paves the way for a new tool for tuning polariton interactions and to move forward into quantum correlated polariton physics

Excitation transfer through thick barriers in asymmetric double-quantum-well structures

The transfer of carriers between two adjacent InxGa1−xAs wells with different thicknesses and separated by a thick GaAs barrier has been measured as a function of temperature for different indium concentrations x. The efficiency of the carrier transfer has been determined by photoluminescence excitation measurements. It is roughly constant at low temperature, and increases for increasing temperatures, going through a maximum between 50 and 70 K. At higher temperatures, where the photoluminescence shows a drastic quenching, also the carrier transfer efficiency decreases rapidly. The thermal escape of carriers out of the narrow well mediates the transfer, quenched at higher temperatures by an increased role of nonradiative recombination centres in the well and/or in the barrier. A comparison with a simple rate equation model supports an ambipolar escape of carriers in cw measurements, a unipolar escape of carriers in time-resolved measurements. This is explained in terms of the different excitation conditions in two types of experiments

Formation and relaxation of exciton-carbon acceptor complexes in GaAs

Photoluminescence excitation (PLE) measurements have been performed in several GaAs-based structures by monitoring the electron-carbon acceptor and the exciton bound to carbon recombinations. In both cases we show that the separate capture of free carriers makes the main contribution to the electron-carbon transition and to the formation of the bound exciton. A dip is indeed observed in the PLE spectra at the energy of the free exciton. The contribution of the bound exciton relaxation to the two-hole transition is pointed out