Coherence of a magnetoexciton condensate in a quantum Hall insulator

The coherent properties of a dense ensemble of triplet cyclotron magnetoexcitons in a quantum Hall insulator near the filling factor $\nu = 2$ have been studied using shear interferometry methods. It has been found that a condensate of magnetoexcitons formed at fairly low temperatures by means of nonresonant photoexcitation has a higher degree of coherence compared to the gas of uncondensed magnetoexcitons: the transverse length of coherence reaches about $10\,\mu$m. The condensate can include up to $20\%$ of all triplet magnetoexcitons.