Activation study of collective excitations of the soliton-lattice phase in the ν=1 double-layer quantum Hall state

We investigate thermal excitations of the pseudospin soliton lattice in the double-layer quantum Hall (QH) state at total Landau-level filling factor ν=1 by detailed measurements of the activation energy gap, where the pseudospin represents the layer degree of freedom. In a tilted magnetic field, the activation energy gap of the double-layer ν=1 QH state shows a minimum near the phase transition point between the commensurate and incommensurate states. From a comparison of the in-plane field dependence of the activation energy gap with theories, we suggest that the minimum in the activation energy gap is due to collective modes of the soliton lattice.