Orbital-transverse density-wave instabilities in iron-based superconductors

TL;DR

This paper introduces a new orbital-transverse density-wave (OTDW) state in multi-orbital systems, explaining its role alongside spin-density-waves in iron-based superconductors and their structural transitions.

Contribution

It reveals the existence of the OTDW state and its significance in understanding the magnetic and structural properties of iron-based superconductors.

Findings

OTDW state exists in multi-orbital systems.

Orbital character influences density responses.

Difference between 1111 and 122 compounds explained by Fermi surface topology.

Abstract

Besides the conventional spin-density-wave (SDW) state, a new kind of orbital-transverse density-wave (OTDW) state is shown to exist generally in multi-orbital systems. We demonstrate that the orbital character of Fermi surface nesting plays an important role in density responses. The relationship between antiferromagnetism and structural phase transition in LaFeAsO (1111) and BaFe$_2$As$_2$ (122) compounds of iron-based superconductors may be understood in terms of the interplay between the SDW and OTDW with a five-orbital Hamiltonian. We propose that the essential difference between 1111 and 122 compounds is crucially determined by the presence of the two-dimensional $d_{xy}$-like Fermi surface around (0,0) being only in 1111 parent compounds.