BRAGG REFLECTION FROM EQUIDISTANT PLANES OF VORTEX SHEETS IN ROTATINGHE-3-A

Recently a new state of rotating superfluid He-3-A, which consists of equidistant planes of vortex sheets, was discovered. Its cw NMR absorp tion spectrum includes a small satellite peak which has the largest re lative frequency shift ever observed in He-3-A. This peak is attribute d to the excitation of a stationary spin wave mode which is localized in the gaps between the vortex sheets. This mode corresponds to the fi rst Bragg reflection from a one-dimensional periodic potential. The fr equency shift provides a measurement of the distance between vortex sh eets. This distance agrees with the prediction of Landau and Lifshitz in 1955.