Quantum Griffiths effects in metallic systems

Abstract

We show that two apparently contradictory theories on the existence of Griffiths-McCoy singularities in magnetic metallic systems (see CASTRO NETO A. H. and JONES B. A., Phys. Rev. 5, 62 (2000) 14975 and MILLIS A. J., MORR D. and SCHMALIAN J., Phys. Rev. B, 66 (2002) 174433) are in fact mathematically equivalent. We discuss the generic phase diagram of the problem and show that there is a non-universal crossover temperature range T* < T < ω0 where power law behavior (Griffiths-McCoy behavior) is expected. For T < T* power law behavior ceases to exist due to the destruction of quantum effects generated by the dissipation in the metallic environment. We show that T* is an analogue of the Kondo temperature and is controlled by non-universal couplings. © EDP Sciences.