CAREER: Quantum Transport and Optoelectronics with Helical Crystals

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Nontechnical abstract:The physical properties of materials, and consequently how those materials may be put to work for the benefit of society, is dictated by which elements compose the material and how each element is arranged within the structure of the material. When the elements selenium or tellurium bond together to form a crystal, the arrangement of the elements is rather unique: the atoms form tiny spiraling chains running in the same direction with many parallel chains weakly bonded together to create the crystal. Given this unusual structure, it is not surprising that many new physical properties could arise. The research team synthesizes these materials and incorporates them into electronic devices that create, control and probe the unusual properties. For example, as electrons travel along the spiraling chains, they are expected to generate a large magnetic field that could be useful for information storage and processing. As another example, stretching the spirals is expected to transform these materials from a semiconductor into a special type of metal in which new and useful quantum mechanical properties emerge. This activity is integrated into a broad scope of educational and community-building efforts aimed at training students to enter the quantum science and technology workforce, communicating physics to the general public, and inspiring young students, particularly those from underrepresented groups, to choose careers in science and engineering.Technical abstract:Topological band theory has revolutionized the understanding of what kinds of quantum states are possible in condensed matter settings, and this understanding has led to the experimental realization of many of these states, including various types of topological insulators and Dirac, Weyl, and Majorana fermions. While these quantum states have been investigated with increasing vigor over many years, the development of devices based on quantum materials remains in its infancy, particularly for Weyl and Majorana systems. Such devices could control, optimize, utilize, and further probe some of these states, as well as create new ones. This project converges materials synthesis, two-dimensional material heterostructures, and quantum device fabrication/measurement to revisit two materials, elemental selenium and tellurium, and probe them in a new light as quantum materials. The objective is to experimentally answer fundamental questions about the properties and capabilities of these materials spanning a broad range of topics: the kinetic magneto-electric effect; Fermi energy tuning, strain modification, and confinement of gapped Weyl materials; and heterostructures of tellurium and layered superconductors as a potential Majorana platform. Answers to these questions have the potential to establish trigonal Se and Te as premier quantum materials impacting a wide range of fundamental and applied topics including spintronics, valleytronics, topological (semi)metals, solar energy harvesting, and (topological) quantum information processing.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.