Pnictides as frustrated quantum antiferromagnet close to a quantum phase transition

TL;DR

This paper investigates the magnetic dynamics of pnictides near a quantum phase transition, proposing that magnetic fluctuations suppress static moments and drive structural transitions, with predictions for experimental verification.

Contribution

It provides a detailed theoretical analysis of magnetic modes in pnictides using self-consistent spin-wave theory, highlighting the role of quantum fluctuations and proposing experimental tests.

Findings

No gapless magnetic mode at the Ne9el wave vector

Magnetic fluctuations strongly reduce static magnetic moments

Structural transition driven by an Ising transition in directional degrees of freedom

Abstract

We present a detailed description of the dynamics of the magnetic modes in the recently discovered superconducting pnictides using reliable self-consistent spin-wave theory and series expansion. Contrary to linear spin-wave theory, no gapless mode occurs at the N\'eel wave vector. We discuss the scenario that the static magnetic moment is strongly reduced by magnetic fluctuations arising from the vicinity to a quantum phase transition. Smoking gun experiments to verify this scenario are proposed and possible results are predicted. Intriguingly in this scenario, the structural transition at finite temperature would be driven by an Ising transition in directional degrees of freedom.