Pump-probe nuclear spin relaxation study of the quantum Hall ferromagnet at filling factor ν = 2

The nuclear spin-lattice relaxation time T ₁ of the ν = 2 quantum Hall ferromagnet (QHF) formed in a gate-controlled InSb two-dimensional electron gas has been characterized using a pump-probe technique. In contrast to a long T ₁ of quantum Hall states around ν = 1 that possesses a Korringa-type temperature dependence, the temperature-independent short T ₁ of the ν = 2 QHF suggests the presence of low energy collective spin excitations in a domain wall. Furthermore, T ₁ of this ferromagnetic state is also found to be filling- A nd current-independent. The interpretation of these results as compared to the T ₁ properties of other QHFs is discussed in terms of the domain wall skyrmion, which will lead to a better understanding of the QHF.