Local defect in metallic quantum critical systems - art. no. 167202

We present a theory of a single point, line, or plane defect coupling to th e square of the order parameter in a metallic system near a quantum critica l point at or above its upper critical dimension. At criticality, a spin dr oplet is nucleated around the defect with its core size determined by the s trength of the defect potential. Outside the core a universal slowly decayi ng tail of the droplet is found, leading to many dissipative channels coupl ing to the droplet and to a complete suppression of quantum tunneling. We p ropose an NMR experiment to measure the impurity-induced changes in the loc al spin susceptibility.