ESR bottleneck effect in the heavy-fermion metal YbRh2Si2

An approach related to the bottleneck effect is proposed for an origin of the electron spin resonance (ESR) of a Kondo ion (Yb3+) in the undoped Kondo-lattice systems YbRh2Si2 and YbIr2Si2. The effects observed for the effective ESR g-factor and the ESR linewidth in YbRh2Si2 are associated with the influence of the Kondo effect and the crystalline electric field splitting of the f-multiplet of ytterbium. A corresponding theory, which predicts the exchange-narrowed ESR linewidths in the temperature range 1-10 K, is discussed. © 2007 Elsevier B.V. All rights reserved