Hidden X: Using spatial and magnetic symmetries to guide first principles search of compounds with hidden quantum properties X

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research and education aimed at discovering new materials with novel electronic and magnetic properties. The validation of abstract physical theories and the development of practical novel technologies both depend on the identification of critical materials that harbor specific properties enabling such applications. The discovery of such special materials has proceeded historically either by lucky accidents, or by time-intensive Edisonian empirical or computational search of many examples. Yet, many unique physical effects are fundamentally enabled not just by specific materials constants, but also by critical symmetry conditions pertaining to the pattern of atomic geometries or arrangement of electronic spins. Textbook symmetry rules, on the other hand, often overlook pertinent possibilities. In this project, the PI will search for “Hidden Effects X”, which refers to the general conditions where some effect X is possible even when the nominal symmetry would apparently disallow it. For example, electronic states with the same momentum but opposite spins can have slightly different energies typically in crystalline materials without inversion symmetry and/or when the material contains heavy elements. In this project, the PI will search for materials in which this slight energy splitting for electrons of different spins occurs under the unexcepted circumstances when the crystal has global inversion symmetry, or when the material contains only light elements, or when the global lattice symmetry conceals the lower local symmetry. A few of such ‘breaking of the textbook rules’ have recently been validated experimentally. This research is expected to reveal and validate many more such possibilities in real materials. The subject matter of this research is instrumental for educating and training students and postdocs to lead the transformation to a durable, vibrant, and fundamental research community that cuts across disciplinary boundaries and creates new ways for materials science and engineering to bring benefits to society. In particular, this award will support the education and training of a postdoctoral research associate in the areas of fundamental condensed matter physics and materials theory. The PI will work with the Center for the Integration of Research, Teaching, and Learning at his institution to encourage postdoctoral researchers to be involved in college-level teaching, preparing them for future STEM faculty positions. TECHNICAL SUMMARY This award supports theoretical and computational research and education aimed at discovering new materials with novel electronic and magnetic properties. In particular, the PI will search for “Hidden Effects X”, which refers to the general conditions where effect X exists even when the nominal global crystalline symmetry would apparently disallow it, or that the enabling symmetry is an easily overlooked local symmetry. This project will focus on three such Hidden X categories, where the enabling symmetries are (i) local real-space site symmetries that enable the Rashba and Dresselhaus spin splitting effects even in globally centrosymmetric compounds, or (ii) unusual spin texture patterns, which are unexpected on the basis of the space group symmetry of the compound, as they are determined by the (lower) symmetry of the specific wavevector, or (iii) magnetic symmetry, which gives rise to a Rashba-like momentum dependent spin splitting in certain antiferromagnets, except that unlike the Rashba effect this can happen even without relativistic physics – such as in the absence of spin-orbit coupling. In addition, the PI will work to formulate theoretically the symmetry conditions enabling the coexistence of different effects in the same compound, such as ferroelectricity and Rashba effect; or Rashba effect and topological insulation. For these Hidden X categories, the PI will (a) determine theoretically the pertinent enabling unexpected symmetries, (b) use them as material selection filters to identify specific compound realizations of such effects, to the benefit of future experiments, and (c) calculate the relevant electronic structure of prototype materials via the Density Functional Theory. This award also supports the education and training of a postdoctoral research associate in the areas of fundamental condensed matter physics and materials theory. The PI will work with the Center for the Integration of Research, Teaching, and Learning at his institution to encourage postdoctoral researchers to be involved in college-level teaching, preparing them for future STEM faculty positions. 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.