Critical Local-Moment Fluctuations, Anomalous Exponents, and ω/T Scaling in the Kondo Problem with a Pseudogap

Experiments in heavy-fermion metals and related theoretical work suggest that critical local-moment fluctuations can play an important role near a zero-temperature phase transition. We study such fluctuations at the quantum critical point of a Kondo impurity model in which the density of band states vanishes as |ϵ|^r at the Fermi energy (ϵ=0). The local spin response is described by a set of critical exponents that vary continuously with r. For 0<r<1, the dynamical susceptibility at the critical point exhibits ω/T scaling with a fractional exponent, implying that the critical point is interacting.