Ab-initio investigation of lattice distortions in response to van der Waals interactions in FeSe

TL;DR

This study uses density functional theory to explore how van der Waals interactions and magnetic disorder influence the lattice structure and electronic properties of FeSe, shedding light on 3D effects and magnetic frustration in superconducting Fe-based chalcogenides.

Contribution

It provides a detailed ab-initio analysis of van der Waals effects and magnetic disorder in FeSe, highlighting their roles in lattice distortions and electronic structure in superconducting materials.

Findings

Van der Waals interactions significantly affect lattice distortions in FeSe.

Paramagnetic disorder influences magnetic states and frustration.

3D effects are crucial for understanding FeSe-based superconductors.

Abstract

The electronic structure in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions and the resulting superconducting gap function. In superconducting Fe-based chalcogenides, there have been controversial results regarding the importance of the $k_z$ dependence of the electronic dispersion, the gap structure and the pairing mechanisms of iron-based superconductivity. Here, we present a detailed investigation of the van der Waals interaction in FeSe and its interplay with magnetic disorder and real space structural properties. Using density functional theory we show that they need to be taken into account upon investigation of the 3-dimensional effects, including non-trivial topology, of FeSe$_{1-x}$Te$_x$ and FeSe$_{1-x}$S$_x$ systems. In addition, the impact of paramagnetic (PM) disorder is considered within the spin-space average approach. Our calculations show that the PM relaxed structure supports the picture of different competing ordered magnetic states in the nematic regime, yielding magnetic frustration.