Formation Mechanism and Low-Temperature Instability of Exciton Rings

The macroscopic rings observed in the photoluminescence patterns of excitons in coupled quantum wells are explained by a mechanism of carrier imbalance, transport, and recombination. The rings originate from the spatial separation of $p$ and $n$ carriers, and occur at the interface of the $p$ and $n$ domains, where excitons are generated. We explore the states of excitons in the ring over a range of temperatures down to $380\mathrm{mK}$ and report a transition of the ring into a periodic array of aggregates, a new low-temperature ordered exciton state.