Kondo physics in the algebraic spin liquid

We study Kondo physics in the algebraic spin liquid, a term recently proposed to describe ZnCu(3)(OH)(6)Cl(2) (Ran et al 2007 Phys. Rev. Lett. 98 117205). Although the spin dynamics of the algebraic spin liquid is described by massless Dirac fermions, this problem differs from the pseudogap Kondo model because the bulk physics in the algebraic spin liquid is governed by an interacting fixed point where well-defined quasiparticle excitations are not allowed. Considering an effective bulk model characterized by an anomalous critical exponent, we derive an effective impurity action in the slave-boson context. Performing a large-N(sigma) analysis with a spin index N(sigma), we find an impurity quantum phase transition from a decoupled local-moment state to a Kondo-screened phase. We evaluate the impurity spin susceptibility and specific heat coefficient at zero temperature, and find that such responses follow power-law dependences due to the anomalous exponent of the algebraic spin liquid. Our main finding is that Wilson's ratio for the magnetic impurity depends strongly on the critical exponent in the zero temperature limit. We propose that Wilson's ratio for the magnetic impurity may be one possible probe to reveal the criticality of the bulk system.