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 = frac(1, 2). Incomplete electronic spin polarization, which has been reported previously for low density 2DESs at ν = frac(1, 2), 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: T₁ T = constant is expected for temperatures T < 1 K. Our measurements show that for temperatures in the range 35 mK < T < 200 mK, T₁ rises less rapidly with falling temperature than this law predicts. This may suggest the existence of alternate nuclear spin relaxation mechanisms in this system. Also, our data allows for an estimate of the composite fermion mass.