Atomic-scale design and synthesis of unconventional superconductors

Abstract

Contemporary challenges in computing and energy technologies motivate an understanding of how quantum, electronic, and magnetic phenomena in materials arise from interactions of electrons in crystal lattices. One such phenomenon, high-temperature superconductivity, harbors immense promise for energy storage, transport, and generation, yet has famously eluded a complete or predictive understanding. One approach to this problem is to use the essential features of existing high-temperature superconductors to blueprint the design of new materials that could host superconductivity. In this dissertation, I present complementary approaches to understand and design unconventional superconductors using materials synthesis at the atomic-level, enabled by the technique molecular beam epitaxy (MBE). My principal focus is on the rare-earth nickel oxides (‘nickelates’), a recently identified class of superconductors inspired by the high-$T_c$ cuprates. Using MBE with electronic and structural characterization techniques, we design a new family of nickelate superconductors. By adjusting the number of layers in the nickelate unit cell, we reveal a complete superconducting dome and correlated phase diagram that emerges from atomic structuring of the crystalline lattice. I also discuss an example of how modern advancements in synthesis and characterization technology can enable critical new insight into older superconducting systems. I show the first experimental band structure of MBE-synthesized LiTi$_2$O$_4$ which provides insight into the strong correlations coexisting with superconductivity. This thesis foregrounds the role of atomically-controlled materials synthesis in traversing quantum and correlated phases and channeling new physics.