Title:	Strong electronic correlations and magnetism in systems containing transition metals and lanthanides
DNr:	SNIC 2021/5-528
Project Type:	SNIC Medium Compute
Principal Investigator:	Igor Dimarco <igor.dimarco@physics.uu.se>
Affiliation:	Uppsala universitet
Duration:	2021-12-01 – 2022-12-01
Classification:	10304 10407
Homepage:	http://fplmto-rspt.org/
Keywords:

Abstract

In this project, we plan to use density functional theory (DFT) and its combination with dynamical mean field theory (DMFT) to pursue two major lines of research. Our first line of research is focused on the nature of Vegard's law in solid solution alloys. Vegard's law establishes that the lattice constant of a binary alloy changes linearly with the concentration, when going from one end-point to the other one. The question we want to address here is how valid is this law at a microscopic level, i.e. for average inter-atomic distances. In a previous study we investigated Zn(S,Se), while now we intend to focus on Cd(S,Se). Exploring these two systems will allow us to see if our conclusions hold for anionic solutions of different compositions, as well as for crystal structures with different symmetries. In addition, we intend to extend the current investigation to other properties, as e.g. the elastic response or the band gap. These projects are done in collaboration with the experimental group of Prof. DD Sarma at the Indian Institute of Science (IIS) of Bangalore, India. All the experimental measurements have already been performed, while the data analysis requires input from our DFT calculations. Our second line of research is focused on the magnetism of systems containing lanthanide elements. We recently completed the implementation of a method to extract the anisotropic contributions to the inter-atomic exchange interaction [PRB 102, 115162 (2020)]. The anti-symmetric part, usually referred to as the Dzyaloshinskii-Moriya interaction, is important for several properties, as e.g. the phase diagram of multiferroics and the texture of skyrmions. We intend to investigate these interactions in lanthanide metals, for both bulk and surface, where an increase is expected due to the reduced symmetry. We believe that the anisotropic terms will be crucial in explaining the helical magnetism exhibited by some elements, as eg. Ho. The Dzyaloshinskii-Moriya interaction can also become very large in pyrochlore lanthanide-based iridates, where it competes with the underlying super-exchange. Other materials where the anisotropic contributions to the inter-atomic exchange are expected to be important are the lanthanide-based double-perovskites. These systems were proposed as candidates for the realization of spin liquids and we intend to clarify this issue with an adequate theoretical investigation. Finally, we intend to focus also on the intra-atomic exchange coupling, which is behind the formation of the magnetic order in many lanthanide-based systems. In a recent study we investigated the isotropic terms in lanthanide adatoms deposited on graphene [PRX 10, 031054 (2020)] and we are currently working to extend our formalism to the anisotropic terms as well. Since these have been traditionally neglected, not much is known. We intend to understand how they depend on the type of adatoms and on the local environment. Since the lanthanide elements include strongly correlated 4f electrons, all these calculations will be performed in DFT as well as in DMFT.