Quantum Complexity in Simple Materials

Abstract: Two-dimensional (2D) materials have received widespread attention over the past 20 years due to their remarkable physical, mechanical and chemical properties, and our ability to integrate them into devices. In this seminar, I will discuss a new approach for realizing long-sought electronic structures of geometrically frustrated lattice models (e.g. kagome and pyrochlore), by “decorating” un-frustrated, primitive lattices with a particular set of atomic orbitals. In the process, we identify the vdW intermetallic compound Pd5AlI2 as the first material to realize the electronic structure of the 2D Lieb lattice – featuring Dirac-like bands intersected by a flat band – persisting in ambient conditions down to the monolayer limit. I will discuss how this unique electronic structure gives rise to compact localized states and bound states in continuum (BICs), which could provide a platform for lossless and topologically protected electronic processes. I will then detail our recent synthesis of CeSiI, the first van der Waals (vdW) metal with a heavy fermion ground state. Conceptually, our synthetic design takes a traditional 3D intermetallic structure and slices it into atomically-thin vdW sheets by incorporating iodine into the structure. The resulting material is cleavable and effectively electronically 2D.

Bio: Xavier Roy is a Professor of Chemistry at Columbia University, specializing in solid-state materials chemistry. Roy earned a Bachelor of Engineering in Chemical Engineering in 2002 and a Master of Applied Science in 2005 from École Polytechnique of Montreal. He completed his Ph.D. at the University of British Columbia in 2011 under the mentorship of Mark MacLachlan as an NSERC Alexander Graham Bell Scholar. After an NSERC postdoctoral fellowship with Colin Nuckolls at Columbia University, Roy joined the Columbia Chemistry faculty in 2013. His research spans the assembly of superatomic clusters into functional materials and the exploration of low-dimensional quantum materials, including two-dimensional van der Waals systems and correlated electron phases. He was promoted to Associate Professor in 2018, tenured in 2020, and became a Full Professor in 2024.