Spin superfluidity and coherent spin precession

Abstract

The spontaneous phase coherent precession of the magnetization in superfluid3He-B was discovered experimentally in 1984 at the Institute for Physical Problems, Moscowby Borovik-Romanov, Bunkov, Dmitriev and Mukharsky and simultaneously explainedtheoretically by Fomin (Institut Landau, Moscow). Its formation is a direct manifestationof spin superfluidity. The latter is the magnetic counterpart of mass superfluidity andsuperconductivity. It is also an example of the Bose–Einstein condensation of spin-waveexcitations (magnons). The coherent spin precession opened the way for investigations ofspin supercurrent magnetization transport and other related phenomena, suchas spin-current Josephson effect, process of phase slippage at a critical value ofspin supercurrent, spin-current vortices, non-topological solitons (analogous toQ-balls in high energy physics) etc. New measuring techniques based on coherent spinprecession made the investigation of mass counterflow and mass vortices possible owing tothe spin–mass interaction. New phenomena were observed: mass–spin vortices, theGoldstone mode of the mass vortex with non-axisymmetric core, superfluid densityanisotropy etc. Different types of coherent spin precession were later found in superfluid3He-Aand 3He-B confined in anisotropic aerogel, in the states with counterflow and in3He with reduced magnetization. Finally, spin superfluidity investigations developed thebasis for a modern investigation of electron spin supercurrent and spintronics.