Bragg reflection from equidistant planes of vortex-sheets in rotating 3He-A
Parts U., Koivimierni J.H., Kriisius M., Ruutu V.M.H., Thuneberg E.V., Volovik G.E.
Recently a new state of rotating superfluid He-A was discovered which consists of equidistant planes of vortex sheets. Its cw NMR absorption spectrum includes a small satellite peak which has the largest relative frequency shift ever observed in 3He-A. We interpret this peak to arise from the excitation of a stationary spin wave mode localized in the gaps between the vortex sheets. The mode corresponds to the first Bragg reflection from a 1-dimensional periodic potential. The frequency shift provides a measurement of the distance between vortex sheets. The distance agrees with the prediction of Landau and Lifshitz in 1955.