Variational Monte Carlo study of the nematic state in iron-pnictide superconductors with a five-orbital model**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274310, 11474287, 11174072, and 91221103) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20104208110001).

Abstract

We perform a variational Monte Carlo study of the nematic state in iron-pnictide superconductors within a realistic five-orbital model. Our numerical results show that the nematic state, formed by introducing an anisotropic hopping order into the projected wave function, is not stable unless the off-site Coulomb interaction V exceeds a critical value. This demonstrates that V plays a key role in forming the nematic state in iron-pnictide superconductors. In the nematic state, the orbital order and the anisotropic spin correlations are consistent with the experimental observations. We argue that the experimentally observed anisotropic magnetic couplings and structural transition are associated with the nematic state and can be understood in a unified framework.