Ultra-short-period superlattices of half-metallic and semiconducting Heusler alloys by combinatorial molecular beam epitaxy

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NON-TECHNICAL SUMMARYThe project is to investigate novel synthesis and characterization of artificially structured layered compounds for the science and applications of information technologies. The artificial layered compounds (ALC) consist of 4 to 7 elements tailored atomic layer by atomic layer thus forming nanoscale chemical compounds that are not available in nature or by other known synthesis methods. They correspond to a new archetype of ferromagnetic materials, which can be engineered to possess novel tunable electronic and magnetic functionalities desired for future quantum information technologies. The research will be focused on exploring the synthesis and characterization of the ALC, investigating the atomic scale structures, and probing the electronic and magnetic properties. The objectives are to realize the ALC with the desired properties and functionalities, elucidate the nature and interplay between structures and properties, and develop means to control and fine-tune these properties through atomic scale synthesis. The potential impact is significant, because the work can establish a pathway for realizing and controlling the electronic and magnetic effects in a new class of materials. The work will not only explore novel materials that can be readily integrated into today's silicon-based technologies, but also can lead to general understanding of the fundamental processes in these complex artificial materials. Education is another key objective of the work. Students will be trained in a wide range of interdisciplinary cutting-edge activities from synthesis to characterization, while the individuals will specialize in several state-of-the-art techniques. These areas are of critical importance scientifically and technologically, especially for future advanced technologies, and in order to maintain the leadership role of the US in these areas, investments in human resources and expertise are critically needed. TECHNICAL SUMMARYThe project is to investigate novel MBE synthesis and characterization of ultra-short-period (USP) superlattices (SLs) consisting of half-metallic and semiconducting Heusler compounds on Si/Ge substrates. USP (defined as one to two primitive-cell size of the constituent compounds) corresponds to a new archetype of ferromagnetic SLs. Such an archetype enables non-equilibrium engineering of band structures and interfacial states but has not been explored experimentally. The aim is to realize more robust and tunable ferromagnetic half-metals (HMs) accompanied by a large and tunable uniaxial perpendicular magnetic anisotropy (PMA). This combination of functionalities and tunability is not present in any currently known materials but is extremely desirable for future quantum information technologies. The research will be focused on exploring the MBE synthesis and characterization, investigating the structural and chemical order, and probing the electronic states, spin polarization, and magnetism. The objectives are to realize robust and tunable ferromagnetic HMs in SLs with at least one non-HM constituent, and elucidate the nature of the minority spin gap and related phenomena, realize PMA in the all Heusler SLs, and elucidate the nature and interplay between structure, magnetism, and interfacial states, and develop means to control and fine-tune spin-dependent states and magnetic anisotropy. The potential impact of the work is significant, because it can establish a pathway for realizing and controlling spin polarized effects and magnetism in Si-compatible epitaxial systems. The work will not only explore novel spin polarized materials that can be readily integrated onto Si-based platform, but also can lead to general understanding of fundamental processes in these complex artificial materials. Education is another key objective of the work. Students will be trained in a wide range of interdisciplinary activities from synthesis to characterization, while the individuals will specialize in several advanced techniques. These areas are of critical importance scientifically and technologically.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.