Recent finding of an {\it unusual} in-plane resistivity anisotropy in the underdoped 122-family at high temperature (T) suggests an orbital nematic (ON) order, posing a challenge to extant theories. The {\it sign} of the anisotropy contradicts expectations from weakly correlated as well as pure spin-only nematic views. Here, we show how such an ON order with accompanying structural distortion arises from {\it residual}, intersite and inter-orbital two-body interactions in an incoherent "bad metal" close to Mottness. Enhancement of orbital-selective incoherence is shown to be necessary for understanding transport anisotropy. Our results suggest that ON order, with subsequent antiferromagnetic order might be the {\it primary} competitor to superconductivity in Fe arsenides.
@article{arxiv.1010.2940,
title = {Theory of Orbital Nematicity in Underdoped Iron Arsenides},
author = {Mukul S. Laad and Luis Craco},
journal= {arXiv preprint arXiv:1010.2940},
year = {2010}
}