The nuclear-spin-relaxation rate $1/T_1$ has been measured in a bilayer electron system at and around total Landau level filling factor $\nu =1$. The measured $1/T_1$, which probes electron spin fluctuations, is found to increase gradually from the quantum Hall (QH) state at low fields through a phase transition to the compressible state at high fields. Furthermore, $1/T_1$ in the QH state shows a noticeable increase away from $\nu =1$. These results demonstrate that, as opposed to common assumption, the electron spin degree of freedom is not completely frozen either in the QH or the compressible states.

• Received 19 October 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.096802