Crossover and Order-Disorder Transition of Two-Dimensional Quantum Antiferromagnets at Low Temperatures

Abstract

We study the low-temperature behavior of quantum antiferromagnets in two space dimensions. Our model is the quantum nonlinear sigma model (NLsM), which is the long-wavelength limit of the two-dimensional quantum Heisenberg model. Introducing fermion fields in NLsM, we propose a model of doped antiferromagnets. We show that renormalization-group theory predicts an order-disorder transition at finite hole concentration. Very small doping changes the temperature dependence of the correlation length from exponential to power law for hole concentration $\delta < \delta_c$. We also discuss a crossover between calssical and quantum regions with varying coupling constant g.

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