Using the Landau Fermi liquid theory we discovered a new propagating transverse spin wave in a paramagnetic system which is driven slightly out of equilibrium without applying an external magnetic field. We find a gapless mode which describes the uniform precession of the magnetization in the absence of a magnetic field. We also find a gapped mode associated with the precession of the spin current around the internal field. The gapless mode has a quadratic dispersion leading to a $T^{3/2}$ contribution to the specific heat. These modes significantly contribute to the dynamic structure function.

• Received 17 February 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.047204