VORTEX SHEET IN SUPERFLUID HE-3-A

A new state of rotating superfluid He-3-A has been found recently. Usu ally superfluids respond to rotation by creating an array of vortex li nes, which are parallel to the rotation axis, and the circulation arou nd them is quantized. In the new state the vorticity is located on a 2 dimensional sheet instead of 1 D lines. The sheet is parallel to the rotation axis z but in the x - y plane it folds to equidistant layers. The distance between the layers is larger but on the same order of ma gnitude as the distance between vortex lines. In contrast to other sup erfluids, the sheet is stable in the A phase because of its internal s tructure. The sheet has as a backbone a topologically stable domain wa ll called soliton, to which non-singular vorticity is hound. Thus it c an exist in spite of its presumably higher energy. The vortex sheet is distinguished by its NMR response, in particular because of its highe r absorption at a characteristic frequency. Experiment and theory on t he vortex sheet are in good agreement.