Optical study on the spin-density wave properties in single crystalline Na$_{1-\delta}$FeAs

TL;DR

This optical study of Na$_{1-eta}$FeAs reveals the presence of a spin-density wave gap that opens with the magnetic transition, supporting the itinerant model of antiferromagnetism in FeAs-based compounds.

Contribution

First optical evidence of SDW gap in Na$_{1-eta}$FeAs, showing its relation to magnetic transition and differences from other FeAs compounds.

Findings

SDW gap observed in optical spectra.

Gap opens at magnetic transition temperature.

Smaller gap and spectral weight redistribution compared to other FeAs compounds.

Abstract

We report an optical investigation on the in-plane charge dynamics for Na$_{1-\delta}$FeAs single crystal. A clear optical evidence for the spin-density wave (SDW) gap is observed. As the structural/magnetic transitions are separated in the Na$_{1-\delta}$FeAs case, we find the SDW gap opens in accordance with the magnetic transition. Comparing with the optical response of other FeAs-based parent compounds, both the gap value 2$\Delta$ and the energy scale for the gap-induced spectral weight redistribution are smaller in Na$_{1-\delta}$FeAs. Our findings support the itinerant origin of the antiferromagnetic transition in the FeAs-based system.