Do quantum dots allow one access to pseudogap Kondo physics?

Abstract

For the last decade, tunable quantum dot systems have allowed the investigation of Kondo physics wherein the quenching of a single spin on an artificial atom affects the conductance. The pseudogap Kondo model featuring a density of states $\rho(\epsilon)$ = C$|\epsilon|^{r}$, introduced by Withoff and Fradkin in 1990 was predicted to exhibit Kondo-like physics above a critical value of the Kondo coupling, J$_c$, which several groups have shown by numerical renormalization group (RG) is finite for r$< {1/2}$. Gonzalez-Buxton {\it{et al}} showed that the strong coupling limit of the particle-hole symmetric model leads to a non-trivial $\frac{\pi (1-r)}{2}$ phase shift at low temperatures indicating incomplete screening of the local moment, while away from particle-hole symmetry one generically flows towards a ground state with $\delta \sim \pi$. We examine the implications of this model for quantum dots whose leads are Fermi-liquid-like, yet possess a tunneling density of states which is suppressed at the Fermi energy as a power law.