NMR study of a canted antiferromagnet in a bilayer quantum Hall system

We investigate static and dynamic properties of electron spins in the bilayer quantum Hall system at total Landau level filling factor ν = 2 by using current-pumped and resistively detected nuclear magnetic resonance (NMR). The measured Knight shift, K_S, of ⁷⁵As nuclei reveals continuous variation of the out-of-plane electronic spin polarization P_z between nearly full and zero as a function of density imbalance between the two layers. Nuclear spin relaxation rate 1 / T₁ indicates that the in-plane spin order accompanied by a gapless low-frequency mode (i.e., the Goldstone mode) develops when P_z varies. These results provide direct information on the spin configuration and the low-energy collective excitations in the canted antiferromagnetic state.