  The nuclear spin-lattice relaxation time T1 of the nu = 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 T1
of quantum Hall states around nu = 1 that possesses a Korringa-type temperature
dependence, the temperature-independent short T1 of the nu = 2 QHF suggests the
presence of low energy collective spin excitations in a domain wall.
Furthermore, T1 of this ferromagnetic state is also found to be filling- and
current-independent. The interpretation of these results as compared to the T1
properties of other QHFs is discussed in terms of the domain wall skyrmion,
which will lead to a better understanding of the QHF.
