Theory of Orbital Nematicity in Underdoped Iron Arsenides

TL;DR

This paper proposes a theory that orbital nematic order, arising from residual interactions in a bad metal near Mottness, explains the unusual resistivity anisotropy in underdoped iron arsenides, challenging previous models.

Contribution

It introduces a novel mechanism for orbital nematic order driven by residual interactions in incoherent metals near Mott transition.

Findings

Orbital nematic order explains resistivity anisotropy.

Residual interactions induce structural distortion.

Orbital nematic order competes with superconductivity.

Abstract

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.