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

Via a resistively detected NMR technique, the nuclear spin-lattice relaxation time T-1 of Ga-71 has been measured in a GaAs/AlGaAs heterostructure containing two weakly coupled 2D electron systems (2DES) at low temperatures, each at Landau level filling nu = (1)/(2). Incomplete electronic spin polarization, which has been reported previously for low density 2DESs at nu = (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: T1T = constant is expected for temperatures T 1 K. Our measurements show that for temperatures in the range 35 mK T 200 mK, T-1 rises less rapidly with failing 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. (c) 2006 Elsevier B.V. All rights reserved.