0 Fe b 19 99 Non - Fermi Liquid Behavior in a Disordered Kondo Alloy Model

We study a mean-field model of a Kondo alloy using numerical techniques and analytic approximations. In this model, randomly distributed magnetic impurities interact with a band of conduction electrons and have a residual RKKY coupling of strength J . This system has a quantum critical point at J = Jc ∼ T 0 K , the Kondo scale of the problem. The T dependence of the spin susceptibility near the quantum critical point is singular with χ(0)− χ(T ) ∝ T γ and non-integer γ. At Jc, γ = 3/4. For J ∼ Jc there are two crossovers with decreasing T , first to γ = 3/2 and then to γ = 2, the Fermi-liquid value. The dissipative part of the time-dependent susceptibility χ′′(ω) ∝ ω as ω → 0 except at the quantum critical point where we find χ′′(ω) ∝ √ω. The characteristic spin-fluctuation energy vanishes at the quantum critical point with ωsf ∼ (1− J/Jc) for J ∼ Jc, and ωsf ∝ T 3/2 at the critical coupling. 75.30.Mb, 74.80.-g, 71.55.Jv Typeset using REVTEX ∗Presently at : Service de Physique de l’Etat Condensé, CEA-Saclay, 91191 Gif-sur-Yvette, France 1