Student Hosted Colloquia: Professor James Rondinelli, Northwestern University
About the Seminar
"Symmetry Breaking and the Design of Quantum Magnets"
Pierre Curie famously stated that “asymmetry is what creates a phenomenon.” This principle underpins the emergence of novel quantum phases in magnetic materials, where symmetry breaking—whether spatial or time-reversal—and relativistic effects such as spin-orbit coupling (SOC) play a central role. Our recent theoretical work explores how these mechanisms can be harnessed to discover new classes of quantum magnets. In this talk, I will focus on complex transition metal nitrides, where the covalent bonding between polarizable nitrogen anions and transition metal cations creates rich interaction landscapes (superexchange, enhanced hopping, and new structure types). In ternary nitrides MnXN2 (X = Si, Ge, Sn) and their cation-ordered variants, I report on our discovery of non-relativistic spin-splitting (NRSS) at the Γ point, even in the absence of SOC—extending the concept of “altermagnetism.” These materials also show promise for ferroelectric behavior, offering multifunctional properties. Additionally, I present electronic structure studies of Ca3CrN3, a compound that combines strong intrachain magnetic interactions, weak interchain coupling, and low dimensionality with S = ½ ions. A novel Ca-mediated superexchange pathway via quasi-one-dimensional zig-zag chains further enhances its potential as a quantum magnet. Together, these findings position quantum nitrides as a compelling and largely unexplored frontier in quantum materials research, forming the natural successor to the widely studied complex oxides.
About the Speaker
James Rondinelli is the Walter Dill Scott Professor and Associate Chair in the Department of Materials Science and Engineering, where he also holds an appointment in the Applied Physics Program. He leads the Materials Theory and Design Group and serves as Director of the Predictive Science and Engineering Design (PS&ED) Program. His research integrates electronic structure theory with materials design, focusing on transition-metal compounds, alloys, and molecules. By uncovering picoscale structure-property relationships, his work advances technologies in structural materials, microelectronics, and quantum computing. Rondinelli has received numerous honors, including the Presidential Early Career Award for Scientists and Engineers (PECASE) and the Materials Research Society (MRS) Outstanding Young Investigator Award. He is a Fellow of both the American Physical Society (APS), where he served as Chair of the Division of Materials Physics, and the American Association for the Advancement of Science (AAAS). He has authored over 290 peer-reviewed publications and holds two patents. Rondinelli earned his B.S. in Materials Science and Engineering from Northwestern University and his Ph.D. in Materials from the University of California, Santa Barbara. Prior to joining Northwestern, he was a Joseph Katz Named Fellow at Argonne National Laboratory and an assistant professor at Drexel University.