Theory of the electron spin resonance in heavy fermion systems with non-Fermi-liquid behavior

The theory of the electron spin resonance (ESR) in heavy fermion systems exhibiting a non-Fermi-liquid behavior is developed. It is shown that for the same values of the g factor of localized and itinerant electrons in the absence of the magnetic anisotropy the ESR signal has a δ-function shape if one does not take into account electron-lattice or electron-nuclear couplings. Magnetically anisotropic electron-electron interactions of localized electrons, together with the hybridization between wave functions of itinerant and localized electrons, yield a shift of the position of the ESR signal and change the linewidth. These changes in the characteristics of the ESR in heavy fermion systems are connected with interactions of low-energy quasiparticles. We have shown that there can be a Fermi-liquid contribution to the linewidth and a shift of the position of the ESR (the effective g factor) and a non-Fermi-liquid one, governed by the quantum critical point. Obtained results are compared with recent experimental ESR data for the heavy fermion compound YbRh₂Si₂.