Ethan McGarrigle: Field-theoretic numerical simulations for studying magnetic materials
Field-theoretic numerical simulations for studying magnetic materials
Abstract: Magnetic materials offer an exciting avenue for realizing exotic quantum disordered ground states, where topological order may emerge instead of conventional magnetic order at low temperatures. In many cases, the apparent disorder stems from the combination of quantum fluctuations and frustration, where competing exchange interactions among spins on the lattice cannot be satisfied. While frustrated Heisenberg models offer a simple microscopic starting point for real magnetic materials, numerical approaches are mostly limited to small system sizes, non-frustrated systems, and zero temperature. Here, I will present a new computational method for studying the thermodynamics of frustrated quantum spin-S systems. Our approach uses an equivalent fieldtheoretic representation of the quantum spin lattice at finite temperature, based on the Schwinger boson coherent state path integral. Considering canonical systems such as square, triangular, and honeycomb lattices, we demonstrate our technique’s ability to access equilibrium spin textures, spinspin correlations, and magnetic properties, which enable the study of phase transitions and quantumclassical comparisons. Finally, we discuss extensions of the method and its current limitations.
Bio: Ethan McGarrigle is a fifth-year Ph.D. candidate and Mitsubishi Chemical Fellow in the Department of Chemical Engineering at UC Santa Barbara. During his Ph.D., he developed firstprinciples “field-theoretic” simulation methods for studying the equilibrium behavior of quantum fluids and magnets under the guidance of Prof. Glenn Fredrickson. His work contributed to the discovery of a highly correlated “spin microemulsion” phase found in spin-orbit coupled, Bose- Einstein condensates. Before coming to UC Santa Barbara, he worked briefly in the biotechnology industry after receiving his B.S. in Chemical Engineering from the Massachusetts Institute of Technology. Currently, his research interests include new computational approaches in statistical physics for studying strongly interacting quantum matter.
