Quantum phase transition in the quantum compass model
Han-Dong Chen, Chen Fang, Jiangping Hu, Hong Mei Yao · Physical Review B · 2007
In this work, we show that the quantum compass model on a square lattice can be mapped to a fermionic model with local-density interaction. We introduce a mean-field approximation where the most important fluctuations, those perpendicular to the ordering direction, are taken into account exactly. It is found that the quantum phase transition point at ${J}_{x}={J}_{z}$ marks a first-order phase transition. We also show that the mean-field result is robust against the remaining fluctuation corrections up to the second order.