Peter Wolfle
University of Karlsruhe
"ELECTRON SPIN RESONANCE IN KONDO SYSTEMS”
Well-defined electron spin resonance (ESR) lines have
been detected recently in several heavy fermion
compounds, in which ferromagnetic correlations appear to be present1. We first discuss2 the theory of ESR for the Kondo impurity system
at temperatures T<<TK (Kondo temperature), where the local spin ESR line
has a width of order TK and therefore unobservably
broad. By contrast, in the Anderson
lattice system in the Kondo regime the ESR linewidth
is narrow, and gets broadened by spin lattice relaxation and quasiparticle interaction processes. We show2 that
the spin lattice induced ESR linewidth is greatly
reduced by an effective mass factor. The quasiparticle
induced linewidth is small in the Fermi liquid
regime, proportional to max(T2,B) (T=temperature, B=Zeeman energy). The total ESR linewidth
is reduced by exchange narrowing induced by a ferromagnetic exchange
interaction. This explains the available ESR data.
[1] C. Krellner
et al., Phys Rev. Lett. 100, 066401 (2008)
[2] E. Abrahams and P. Woelfle, Phys. Rev. B78, 104423 (2008)