Field-dependent collective ESR mode in YbRh2Si2

Electron spin resonance (ESR) experiments in YbRh2Si2 Kondo lattice (TK≃25K) at different field/frequencies (4.1≤ν≤34.4GHz) and H⊥c revealed: (i) a strong field dependent Yb3+ spin-lattice relaxation, (ii) a weak field and T-dependent effective g-value, (iii) a 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 that the ESR signal in YbRh2Si2 may be due to a coupled Yb3+-conduction electron resonant collective mode with a subtle field-dependent spins dynamic.