We discuss quantum phase transitions in the pseudogap Kondo problem, which describes a magnetic moment coupled to conduction electrons with a power-law density of states, rho(omega) ~ |omega|^r. We show that different perturbative expansions, together with renormalization group techniques, provide effective low-energy field theories for the relevant critical fixed points. In particular, we review expansions near the lower-critical and upper-critical dimensions of the problem, being r=0 and r=1, respectively.
@article{arxiv.cond-mat/0406318,
title = {Critical theories for the pseudogap Kondo problem},
author = {Lars Fritz and Marijana Kircan and Matthias Vojta},
journal= {arXiv preprint arXiv:cond-mat/0406318},
year = {2007}
}