Hidden SDW order and effective low-energy theory for FeAs superconductors

TL;DR

This paper introduces an effective model for FeAs superconductors based on local SDW order, explaining how doping influences magnetic order and superconductivity through Fermi surface nesting and kinetic energy competition.

Contribution

It presents a novel low-energy theory linking local SDW order with superconductivity and magnetic fluctuations in FeAs materials.

Findings

Weak SDW order forms in undoped cases due to Fermi surface nesting.

Unstable long-range SDW order can lead to d-wave superconductivity upon doping.

Local SDW order protects low-energy physics and influences electron behavior.

Abstract

We propose a simple effective model to describe FeAs superconductors. This model is based on the assumption of a local spin-density-wave (SDW) order, with its magnetization direction allowed to fluctuate. It is shown that the long-range order with momentum Q=(\pi ,\pi) is generally unstable in competing with the kinetic energy of the charge carriers. A true weak SDW order is formed in the undoped case with an additional momentum shift Q_s=(\pi, 0) due to the peculiar Fermi surface nesting. In the doped case, the unstable long-range order driven by kinetic energy can naturally result in a d-wave superconducting condensation. Such low-energy physics is protected by the presence of the local SDW which sustains some kind of "Mott gags" for the multiband d-electrons near the Fermi energy.