Collaborative Research: Atomically thin topological insulators via confinement heteroepitaxy

Nontechnical Description

The dawn of quantum computing is rapidly developing with the potential to completely transform the field of computation. However, current quantum computers based on superconductors, ions, or atoms are prone to error due to imperfections. The solution to this grand challenge is to use new, engineered materials which are inherently immune to these imperfections. However, key questions remain regarding how to make a material that integrates the demanding properties needed to achieve superior performance in a technologically relevant manner. The principal investigators have created a new method to make ultra-thin metals, and this project focuses on understanding the microscopic properties of such metals, specifically bismuth and lead. The investigators will evaluate the impact of thinning these materials down to just a few atoms thick to explore how their properties change when they are manipulated at the atomic-scale. Beyond the scientific impact, this collaborative project will provide interdisciplinary research training for underrepresented graduate students, to broaden participation in science and engineering programs. The project will also develop a unique industry/university consortium to impart the importance of safety in industrial and research settings. This will not only better train future scientists for post-graduate careers in industry, but will also improve safety preparedness in academia.

Technical Description

The creation of a quantum spin Hall insulator (QSHI) by reducing the dimensionality of a topological insulator from 3D to 2D could provide a unique, robust route to achieving topological superconductivity. This project will investigate the atomic-scale physical, chemical and electronic properties of 2D bismuth (Bi) and lead (Pb). Lead and bismuth exhibit very strong spin-orbit interactions, and exceptionally robust and easily accessible topological insulator properties that may enable the design of groundbreaking electronic devices with dissipationless spin currents, and the realization of Majorana bound states. Furthermore, these elements exhibit unconventional superconductivity, and could be combined with ferromagnetic materials, suggesting the possibility of creating a Pb-based topological superconductor. The investigators enable the study by synthesizing atomically thin, two-dimensional forms of these materials prepared via confinement heteroepitaxy (CHet) – a novel intercalation process that stabilizes 2D forms of 3D materials developed by the PIs. The SiC/graphene interface passivation is investigated before, during and after synthesis to understand how interface reconstruction can enable in-situ removal of the graphene cap for direct characterization access to the 2D-Bi and Pb. Additionally, removing the graphene cap enables direct functionalization of the 2D metal to explore how modifying the surfaces of 2D-Bi and Pb changes their underlying physical properties, including bonding and electronic character. Finally, the project is developing a mechanistic understanding of how the structure and interfacial interactions with SiC and graphene impact electronic structure of 2D-Bi and 2D-Pb and elucidate how they differ from thin films deposited by traditional methods.

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.