Observations of a glass transition in a quasi-two-dimensional electron-hole system

Using time-resolved photoluminescence experiments and Monte Carlo simulatio n, we identify two distinct temperature regimes in the energy relaxation of excitons in a GaAs/AlGaAs double quantum structure. Below a critical tempe rature. the system is glassy and exhibits slow, nonexponential energy relax ation to the longest times observed. At higher temperatures, the system ach ieves thermal equilibrium in finite time. The transition between these regi mes is marked by a dramatic critical behavior: a dynamical broadening of th e energy distribution at the glass temperature. Simulations reproduce this critical behavior and allow for the first time the determination of the den sity of localized states.