NSF Award
2323858
Non-technical Description: Materials discovery requires new tools that enable design principles. The properties of many technologically relevant materials, such as perfect conductivity in superconductors and electric current control of magnets, arise from the spin of electrons. This project will use pseudospin - a quantum mechanical degree of freedom analogous to electron spin - as a new tool for materials discovery. The research will follow the collaborative and iterative closed-loop Materials Genome Initiative approach by combining analytic and predictive computational theory, together with epitaxial growth of materials one atomic layer at a time, and characterization using advanced microscopy and spectroscopy techniques. This project will develop new guiding principles based on controlling pseudospin in materials design, a paradigm shift in quantum materials discovery that will enable both superconductors that can sustain high magnetic fields and novel magnets. This activity will provide training for the next-generation quantum workforce. <br/><br/>Technical Description: This project aims to develop pseudospin control as a materials design tool for discovering new magnetic states and superconductivity. The concept of pseudospin derives from the two-fold Kramers degeneracy of Bloch electrons when time-reversal and inversion symmetries are present. Normally, pseudospin behaves as spin-1/2 under rotations, driving much of our understanding of Cooper pairing in superconductors, Stoner ferromagnetism, and spin control by Zeeman fields. However, for crystals with non-symmorphic space group symmetry, pseudospin can behave very differently than normal spin-1/2. This can lead to novel magnetic states, including altermagnets and odd-parity multipole magnets, and qualitatively alter the superconducting response to magnetic fields. This project will initially develop a new and comprehensive theory of this novel pseudospin. Then density functional calculations will be used to guide the search for materials with desirable properties driven by non-spin-1/2 pseudospin, including high-field superconductors and novel magnets. Thin films of candidate materials will be grown by molecular beam epitaxy on various perovskite oxide substrates, which offer tunability of magnetic and superconducting properties by tailoring lattice strain, proximity effects, charge doping, and electric and optical gating. The experimental demonstration of, for example, crystal Hall effects in altermagnets and the nonlinear Hall effect in odd-parity magnets will provide both a means to validate the theoretical predictions and a path to synthesize new magnetic phases.<br/><br/>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.
