Z. Vörös

Long-distance diffusion of excitons in double quantum well structures.

In this Letter we report on lateral diffusion measurements of excitons at low temperature in double quantum wells of various widths. The structure is designed so that excitons live up to 30 micros and diffuse up to 500 microm. Particular attention is given to establishing that the transport occurs by exciton motion. The deduced exciton diffusion coefficients have a very strong well width dependence, and obey the same power law as the diffusion coefficient for electrons.

Trapping long-lifetime excitons in a two-dimensional harmonic potential

Abstract We report an important step forward for the goal of unambiguous observation of Bose–Einstein condensation of excitons in semiconductors. We have demonstrated a system in which excitons live for microseconds, much longer than their thermalization time, move over distances of hundreds of microns, and can be trapped in a harmonic potential exactly analogous to the traps for atomic condensates. We also report recent results of a new method for observing evidence of Bose–Einstein condensation, by angular resolution of the emitted luminescence.

QUANTUM WELL EXCITONS AT LOW DENSITY

In this paper, we give an overview of our recent work in the quest for Bose–Einstein condensation of spatially indirect excitons. After discussing the benefits of using such particles as the participants of this intriguing quantum phase transition, we turn to the experimental difficulties and obstacles in the way to a successful realization of excitonic BEC.

Considerations on equilibration of two-dimensional excitons in coupled quantum well structures

In this paper we discuss the issues of the equilibration dynamics of spatially indirect two-dimensional excitons in a coupled quantum well structure, in particular those trapped by an in-plane harmonic potential trap. We discuss the relative timescales for several processes. In the experiments with an in-plane trap, we can use the size of the exciton cloud as a measure of the temperature of particles. At low lattice temperatures the exciton temperature is higher than that of the lattice, even long after equilibrium has obviously been reached. We discuss the effects that can be responsible for this.

Trapping of 2D excitons and polaritons

In this paper we discuss a trapping method of quantum well excitons and polaritons. The trapping mechanism is based on the deformation of the band structure. Through drift experiments, first we demonstrate that both excitons and polariton react to the force of the trap and fill it up. In the case of excitons, this leads to a true equilibrium configuration, and thus the temperature of the gas can directly be measured.

Lateral diffusion of excitons in double quantum well structures

We report on lateral diffusion measurements of excitons in GaAs/AlGaAs double quantum wells of various width. In wide quantum wells the excitons have lifetime up to 10 microseconds and diffusion length up to 500 microns.