Abstract: In frustrated magnetic systems with a subextensive number of classical ground states, quantum zero-point fluctuations can select a unique long-range ordered state, a celebrated phenomenon referred to as order by quantum disorder (ObQD). For frustrated spin-1/2 models, unbiased numerical methods able to expose ObQD are necessary. We show that ObQD can be identified from exact diagonalization calculations through an analysis akin to the Anderson tower of states associated with spontaneous symmetry breaking.
By defining an effective quantum rotor model, we describe the competition between ObQD-induced localization of the rotor and its tunneling between symmetry-related ground states, identifying the crossover length scale from the finite-size regime where the rotor is delocalized to the infinite system-size limit where it becomes localized.
This rotor model relates the characteristic splittings in the exact diagonalization energy spectrum to the ObQD selection energy scale, providing an estimate that can be compared to spin wave calculations. We demonstrate the general applicability of this approach in one-, two-, and three-dimensional frustrated spin models that exhibit ObQD.
S. Khatua, G. C. Howson, M. J. P. Gingras, J. G. Rau, Physical Review Letters 136, 146702 (2026)
About the Speaker
Professor Rau is an associate professor at the University of Windsor specializing in theoretical condensed matter physics.
His research is primarily in quantum magnetism with some connections to strongly correlated systems. Professor Rau studies how frustration, many-body effects and quantum mechanics can produce emergent behavior in real materials.
His current interests include order-by-disorder, alter-magnetism, spin dynamics, and frustration in anisotropic systems.