Europhys. Lett.
Volume 71, Number 5, September 2005
Page(s) 790 - 796
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 22 July 2005
Europhys. Lett., 71 (5), pp. 790-796 (2005)
DOI: 10.1209/epl/i2005-10138-7

Quantum Griffiths effects in metallic systems

A. H. Castro Neto1 and B. A. Jones2

1  Department of Physics, Boston University - Boston, MA 02215, USA
2  IBM Almaden Research Center - San Jose, CA 95120-6090, USA

received 2 May 2005; accepted 27 June 2005
published online 22 July 2005

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. B 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 $T^*<T<\omega_0$ 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.

71.27.+a - Strongly correlated electron systems; heavy fermions.
75.20.-g - Diamagnetism, paramagnetism, and superparamagnetism.
75.40.-s - Critical-point effects, specific heats, short-range order.

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