A non-conventional approach to study the quenched impurity effects on quantum criticality

A non-conventional point of view is used to explore the still unclear role played by the competition between quenched disorder and quantum fluctuations in systems which exhibit a quantum phase transition in the clean limit. The approach consists in averaging over quantum degrees of freedom and next in applying the renormalization group transformation to the resulting effective classical random action. It emerges that, below four dimensions, the quantum criticality appears to be controlled by the classical random fixed point. (c) 2006 Elsevier B.V. All rights reserved.