Theory of Electron Nematic Order in LaOFeAs

TL;DR

This paper models the magnetic and structural phase transitions in LaOFeAs using a quantum Heisenberg model, revealing a nematic phase that explains experimental observations of symmetry breaking and magnetic order.

Contribution

It introduces a theoretical framework showing how magnetic fluctuations induce a nematic phase, linking structural and magnetic transitions in LaOFeAs.

Findings

Identification of a nematic phase between symmetric and magnetic phases.

Correlation of structural transition with incipient magnetic order.

Agreement with neutron scattering experimental results.

Abstract

We study a spin $S$ quantum Heisenberg model on the Fe lattice of the rare-earth oxypnictide superconductors. Using both large $S$ and large $N$ methods, we show that this model exhibits a sequence of two phase transitions: from a high temperature symmetric phase to a narrow region of intermediate ``nematic'' phase, and then to a low temperature spin ordered phase. Identifying phases by their broken symmetries, these phases correspond precisely to the sequence of structural (tetragonal to monoclinic) and magnetic transitions that have been recently revealed in neutron scattering studies of LaOFeAs. The structural transition can thus be identified with the existence of incipient (``fluctuating'') magnetic order.