Fermi liquid instabilities in the spin channel

We study the Fermi-surface instabilities of the Pomeranchuk type Sov. Phys. JETP 8 361 (1959) in the spin-triplet channel with high orbital partial waves [F_l^a(l>0)]. The ordered phases are classified into two classes, dubbed the α and β phases by analogy to the superfluid ³He A and B phases. The Fermi surfaces in the α phases exhibit spontaneous anisotropic distortions, while those in the β phases remain circular or spherical with topologically nontrivial spin configurations in momentum space. In the α phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have a nearly isotropic underdamped dispersion relation at small propagating wave vectors. Due to the coupling to the Goldstone modes, the spin-wave spectrum develops resonance peaks in both the α and β phases, which can be detected in inelastic neutron-scattering experiments. In the p-wave channel β phase, a chiral ground-state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.