  Time-dependent capacitance measurements reveal an unstable phase of electrons
in gallium arsenide quantum well that occurs when two Landau levels with
opposite spin are brought close to degeneracy by applying a gate voltage. This
phase emerges below a critical temperature and displays a peculiar
non-equilibrium dynamical evolution. The relaxation dynamics is found to follow
a stretched exponential behavior and correlates with hysteresis loops observed
by sweeping the magnetic field. These experiments indicate that metastable
randomly-distributed magnetic domains are involved in the relaxation process in
a way that is equivalently tunable by a change in gate voltage or temperature.
