| Summary: | 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- and 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.
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