Korringa-like nuclear spin-lattice relaxation in a 2DES at ν=1/2

Via a resistively detected NMR technique, the nuclear spin-lattice relaxation time T1 of 71Ga has been measured in a GaAs/AlGaAs heterostructure containing two weakly coupled 2D electron systems (2DES) at low temperatures, each at Landau level filling ν=12. Incomplete electronic spin polarization, which has been reported previously for low density 2DESs at ν=12, should facilitate hyperfine-coupled nuclear spin relaxation owing to the presence of both electron spin states at the Fermi level. Composite fermion theory suggests a Korringa-law temperature dependence: T1T=constant is expected for temperatures T<1K. Our measurements show that for temperatures in the range 35mK