Theory of Many-Body Effects on Conduction-Electron Spin Resonance in ag-Anisotropic Metal

The variation of $g$ over the Fermi surface leads to a breakdown of Larmor's theorem when scattering is too slow to motionally narrow conduction-electron spin resonance. We show that electron correlations lead to a collective mode whose position is not that of motionally narrowed conduction-electron spin resonance, and whose width would be zero in the absence of scattering. The shift and width of the collective mode are discussed in general and calculated in one experimentally interesting regime.