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FRINATEK-Fri prosj.st. mat.,naturv.,tek

First-principles modeling of magnetic topological materials from relativistic hybrid density functional theory

Alternative title: Modellering av magnetiske topologiske materialer ved bruk av relativistisk hybrid tetthetsfunksjonalteori fra første prinsipper

Awarded: NOK 3.4 mill.

Topological materials form a class of materials that exhibit remarkable properties protected by symmetries of fundamental physical laws. For instance, topological insulators conduct electricity only on their surface, while the "inside" of the material is insulating. Due to the symmetry protection, the electronic states that enable the surface conduction of electricity are immune to impurities found in natural samples. Such properties often originate in the coupling of the electron's spin with its orbital motion. This so-called spin-orbit coupling is a consequence of quantum mechanics combined with the Einstein's special theory relativity, and is significantly enhanced for materials containing heavy elements, such as tin, tellurium, tungsten, gold, mercury, or bismuth. Theoretically predicting and identifying potential topological materials requires solving complicated quantum mechanical equations using supercomputers. A description that is consistent with relativity and includes the spin-orbit coupling poses additional challenges to the theoretical models and needs much more computational time. MagneToMat targets topological properties of materials with an ordered arrangement of magnetic spins, called magnetic materials. These materials offer many practical applications, for example, as components of quantum computers, as memory devices with high density of information storage, and in controlling magnetic states with currents. The goal of MagneToMat is to deliver a reliable and efficient method that enables systematic studies of novel material properties and predictions of new magnetic solids from first principles. The project's objectives will be carried out in cooperation with Prof. A. Bansil and his group in Boston that has a strong expertise in modeling topological materials and an extensive network of collaborators among the theoretical as well as experimental groups. The project activities include developing tools for analyzing effects of the spin-orbit coupling in magnetic solids and applying the tools in the search for new promising materials.

Reliable theoretical predictions of new materials and their properties depend on methods based on first principles. Such approaches aim to solve fundamental quantum mechanical equations and are free of undetermined model parameters. Topological materials exhibit a large variety of novel properties, with many possible applications in spintronics and quantum computing. However, majority of first-principles modeling of such properties has been performed on non-magnetic materials. This is due to significant challenges that arise in the theoretical descriptions of such materials. Topological materials often contain heavy elements, and thus their electronic structure requires a full relativistic treatment that incorporates effects of special theory of relativity. Within the relativistic framework, the spin and orbital degrees of freedom of an electron are coupled, which significantly increases the methodological complexity and computational cost. Magnetic materials pose further challenges to the methods due to large demands on the (magnetic) unit cell size, as well as limitations introduced by density functional theory. Hence, topological properties of realistic materials containing heavy elements remain largely unexplored. The MagneToMat project aims to solve both these challenges by formulating and implementing a relativistic first-principles theory based on a local atom-centered basis (Gaussian-type orbitals) and extending density functional theory to include hybrid functionals containing a portion of multicomponent exact exchange interaction. Within the scope of this project, the developed method will be applied to explore new two- and three-dimensional magnetic materials and their properties. The findings of this projects can be used to understand realistic solids and guide experiment in growing new samples.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek