Magnetic field dependence and bottlenecklike behavior of the ESR spectra in YbRh2Si2

Electron spin resonance (ESR) experiments at different fields or frequencies (4.1≤ν≤34.4 GHz) in the Kondo lattice (TK ≃25 K) YbRh2Si2 single-crystal compounds confirmed the observation of a single anisotropic Dysonian resonance with g⊥c ≅3.55 and no hyperfine components for 4.2≲T≲20 K. However, our studies differently reveal that (i) the ESR spectra for H⊥c show strong-field-dependent spin-lattice relaxation, (ii) a weak-field and temperature-dependent effective g value, (iii) a dramatic suppression of the ESR intensity beyond 15% of Lu doping, and (iv) a strong sample and Lu-doping (≤15%) dependence of the ESR data. These results suggest a different scenario where the ESR signal may be associated to a coupled Yb3+-conduction electron resonant collective mode with a strong bottleneck and dynamiclike behavior. © 2009 The American Physical Society