We study the phase diagram and the quantum phase transitions of a site-diluted two-dimensional O(3) quantum rotor model by means of large-scale Monte Carlo simulations. This system has two quantum phase transitions: a generic one for small dilutions and a percolation transition across the lattice percolation threshold. We determine the critical behavior for both transitions and for the multicritical point that separates them. In contrast to the exotic scaling scenarios found in other random quantum systems, all these transitions are characterized by finite-disorder fixed points with power-law scaling. We relate our findings to a recent classification of phase transitions with quenched disorder according to the rare region dimensionality, and we discuss experiments in disordered quantum magnets.
T. Vojta and R. Sknepnek, "Quantum Phase Transitions of the Diluted O(3) Rotor Model," Physical Review B: Condensed Matter and Materials Physics, American Physical Society (APS), Jan 2006.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.74.094415
National Science Foundation (U.S.)
Natural Sciences and Engineering Research Council of Canada
University of Missouri Research Board
Keywords and Phrases
Monte Carlo Methods; Critical Points; Magnetic Transitions; Percolation
Article - Journal
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