We consider the influence of a quenched random field on the critical behavior of a quantum spherical model at the zero-temperature quantum phase transition. We find a complete solution of the model for arbitrary translationally invariant pair interactions. It turns out that the critical behavior for zero as well as finite temperatures is dominated by static random field fluctuations rather than by quantum or thermal fluctuations. Therefore the critical behavior close to the zero-temperature quantum phase transition is identical to that close to a finite-temperature transition. The system does not show a crossover from quantum to classical behavior.
T. Vojta and M. Schreiber, "Critical Behavior of a Quantum Spherical Model in a Random Field," Physical Review B - Condensed Matter and Materials Physics, vol. 53, no. 13, pp. 8211-8214, American Physical Society (APS), Apr 1996.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.53.8211
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