CAREER: Structural Control of Spin-Orbit Coupling

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education activities that aim to develop fundamental understanding of the interplay between the orbital and spin degrees of freedom of electrons, called the spin-orbit coupling, in solid state crystalline materials. While every atom, and hence every material, has some spin-orbit coupling, the symmetry of the arrangement of atoms in certain crystalline compounds may lead to specific types of spin-orbit effects that are beneficial for future technological applications. These applications include the spin transistor, which enables the control of the spin-current of the electrons. If realized on a commercial scale, the spin transistor could lead to a spintronics revolution in the electronics industry. The PI and his team will utilize computer simulations and a field of mathematics, referred to as the group theory, to understand how the crystal structure can be externally manipulated to induce different spin-orbit effects. This fundamental understanding is expected to lead to the prediction of new materials that could help realize spintronics technologies on a commercial scale. In addition to research efforts, this award also supports the training and education of graduate and undergraduate students and the development of a new teaching approach for concepts related to crystal structures. This new approach will take advantage of the widespread and low cost availability of 3D printers, which will be used to make models that will facilitate learning for undergraduate and graduate students. The computer files for these models will be disseminated publicly along with a set of accompanying exercises for the students. TECHNICAL SUMMARY This award supports research and educational activities that aim to develop fundamental understanding on the origin of different spin-orbit coupling related effects in nonmagnetic crystalline materials and the connection of these effects with the space group symmetry. These include the well-known Rashba and Dresselhaus effects, as well as numerous higher order terms in the electronic Hamiltonians. While there are many spintronics device proposals that take advantage of spin-orbit coupling, there is a gap between the model Hamiltonians and the real materials where the desired spin-orbit effects are often small, or the Hamiltonians have higher order terms that complicate the observed phenomena. This award aims to fill this gap by extracting realistic models with materials specific parameters by a combination of first principles calculations (Density Functional Theory and Dynamical Mean Field Theory) and group theory. Group representations will be utilized to elucidate the coupling between crystal structural distortions and the electronic structure, and novel means to achieve the electric field control of spin-dependent electronic structure and materials that realize these means will be discovered. Additionally, the effect of strong spin-orbit coupling in the crystal structures of strongly correlated transition metal oxides and their phonon spectra will be studied using first principles correlated electron approaches. In addition to supporting the education of a PhD student, the award also provides support for the development of educational materials for more effective teaching of crystallographic concepts to materials science, physics, and chemistry students. The educational part of the award aims to develop low cost educational models of crystal structures and tools for teaching symmetry-related concepts. This will be achieved by using commercially available setups for additive manufacturing. With the help of an undergraduate student, the PI will develop a library of 3D symmetry and structure models, which can be produced at low cost by widely available 3D printers. This library will be made publicly available along with a set of accompanying exercises.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.