Abstract
We examine the low-temperature critical dynamics of two ferromagnetic models of the disordered state having "mode-mode coupling." A method is developed to incorporate mode-mode coupling contributions in an momentum-space renormalization-group analysis of a quantum system. For each model, both quantum and classical critical regions may exist. The characteristic dimensionality changes from classically to in the quantum limit. The dynamic critical index associated with the quantum fixed point is . The scaling behavior of the spin transport coefficient is examined in the limit. We discuss the properties of the quantum-to-classical crossover, including the "metastable" nature of the quantum fixed points.
- Received 26 February 1979
DOI:https://doi.org/10.1103/PhysRevB.22.236
©1980 American Physical Society