CDS&E: Computational Studies of Weyl Semimetals: Disorder, Correlations and Topological Properties

University Of California-Davis, Davis CA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports computational and theoretical research and education towards discovering and studying the properties of new Weyl semimetals. These are new types of materials that have been recently proposed theoretically and are now beginning to be discovered. They are very poor conductors in their bulk but have highly conductive metallic surfaces. These materials are special in that their surface enjoys what is called topological protection, meaning that it cannot be changed without destroying the bulk material. In most materials, surfaces can be chemically altered as they tend to pick up impurities from the environment, which in turn interfere with how materials conduct electricity, a crucial feature for applications in any electronic device. However, the topologically protected surfaces of Weyl semimetals are robust to impurities. This research project aims to develop methods for finding new Weyl semimetals, and for understanding their properties using computer-based simulations. The close competition between various degrees of freedom of the electrons in these materials makes their study particularly challenging, but also holds great promise for new functionalities. The research will lead to new methods, algorithms, and software that will enhance and simplify our ability to carry out material-specific studies and to promote the gradual improvement of materials by computer-aided design, thus shortening currently expensive and inefficient trial-and-error procedures. Developing scientific software tools that incorporate computer programs into a user-friendly interface lowers the barrier to entry for the computational exploration of the properties of quantum materials. The development of these user-friendly interfaces will also facilitate the teaching of elementary theories of topological materials at advanced undergraduate and graduate levels, thereby enhancing University curricula. TECHNICAL SUMMARY This award supports the development of computational approaches that are based on density-functional theory combined with dynamical-mean-field and perturbation theories, which will allow finding new topological semimetals and studying their single-particle spectra, transport, magnetic, and superconducting properties. Guided by similarities between crystal structures and topological features of known systems, realizations of the band inversion mechanism between electronic states of different parity, hybridization effects between partially filled strongly correlated states with filled or empty topological energy bands, chemical valence arguments and physical intuition, a high-throughput screening of materials for their topological properties will be performed in the infinite space of chemically allowed compounds using computer-based simulations. These findings will allow identifying new topological materials, such as Weyl semimetals, and, in particular, those with only Weyl nodes and no other Fermi surface states. Such discoveries could motivate further experimental studies of the chiral anomaly and topological superconductivity. Theoretical and computational approaches to predict and study complex behavior in these systems would potentially influence the design of quantum materials with unique characteristics that rely on topological protection of states, which are at the frontier of materials science. The research will lead to new methods, algorithms, and software that will enhance and simplify our ability to carry out material-specific studies and to promote the gradual improvement of materials by computer-aided design, thus shortening currently expensive and inefficient trial-and-error procedures. Developing scientific software tools that incorporate computer programs into a user-friendly interface lowers the barrier to entry for the computational exploration of the properties of quantum materials. The development of these user-friendly interfaces will also facilitate the teaching of elementary theories of topological materials at advanced undergraduate and graduate levels, thereby enhancing University curricula. 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.