Effect of spatial resolution on the estimates of the coherence length of excitons in quantum wells

TL;DR

This paper investigates how optical resolution limits affect measurements of exciton coherence length in quantum wells, refining previous estimates and confirming that low-temperature coherence enhancement remains valid.

Contribution

It introduces a correction method for diffraction effects in coherence length measurements, improving accuracy of previous experimental estimates.

Findings

Diffraction limits can significantly affect coherence length estimates.

The corrected coherence length is the quadratic sum of actual length and diffraction correction.

Low-temperature exciton coherence enhancement remains valid after correction.

Abstract

We evaluate the effect of diffraction-limited resolution of the optical system on the estimates of the coherence length of 2D excitons deduced from the interferometric study of the exciton emission. The results are applied for refining our earlier estimates of the coherence length of a cold gas of indirect excitons in coupled quantum wells [S. Yang et al., Phys. Rev. Lett. 97, 187402(2006)]. We show that the apparent coherence length is well approximated by the quadratic sum of the actual exciton coherence length and the diffraction correction given by the conventional Abbe limit divided by 3.14. In practice, accounting for diffraction is necessary only when the coherence length is smaller than about one wavelength. The earlier conclusions regarding the strong enhancement of the exciton coherence length at low temperatures remain intact.