We study the influence of quenched disorder on quantum phase transitions in itinerant magnets with Heisenberg spin symmetry, paying particular attention to rare disorder fluctuations. In contrast to the Ising case where the Landau damping of the spin fluctuations suppresses the tunneling of the rare regions, the Heisenberg system displays strong power-law quantum Griffiths singularities in the vicinity of the quantum critical point. We discuss these phenomena based on general scaling arguments, and we illustrate them by an explicit calculation for O(N) spin symmetry in the large-N limit. We also discuss broad implications for the classification of quantum phase transitions in the presence of quenched disorder.
T. Vojta and J. Schmalian, "Quantum Griffiths Effects in Itinerant Heisenberg Magnets," Physical Review B: Condensed Matter and Materials Physics, American Physical Society (APS), Jan 2005.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.72.045438
Iowa State University
National Science Foundation (U.S.)
United States. Department of Energy
Keywords and Phrases
Heisenberg uncertainty principle; Phase transformations (Statistical physics)
Article - Journal
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