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Journal of Magnetism and Magnetic Materials

Study of critical phenomena of quantum spin systems by spin-cluster approximation series

Hiroshi Mano

Published Dec 1, 1990• 19 citations
Publisher
DOI
10.1016/s0304-8853(10)80100-3

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A cluster-effective-field theory, called the double-cluster approximation, is formulated for quantum spin systems at T=0. Combining this approximation with the coherent-anomaly method (CAM), critical phenomena in such systems can be analysed. To test their theory, the authors have estimated the critical points and critical exponents of the one-dimensional S=1/2 transverse Ising model and the one-dimensional S=1/2 XZ model. The estimates are in good agreement with the exact solutions. These results show that the CAM approach is useful in treating zero-temperature phase transitions in quantum spin systems.