Professor Jeffrey Rau
Windsor University
Pseudo-Goldstone Modes and Order-by-Disorder
Location: 4138 Physics Research Building
Faculty Host: Yuan-Ming Lu
Abstract: In systems with competing interactions, continuous degeneracies can appear which are accidental, in that they are not related to any symmetry of the Hamiltonian. Accordingly, the “pseudo”-Goldstone modes associated with these degeneracies are also unprotected. Indeed, through a process known as “order-by-disorder” fluctuations can lift the degeneracy and induce a gap for these modes. In this talk, I will discuss how these pseudo-Goldstone gaps arise in frustrated magnets when the fluctuations are (i) quantum mechanical and (ii) thermal in origin. I will show that the gap can be exactly computed at leading order using an effective picture where the soft modes move in a potential generated by the fluctuation-induced free energy. Using explicit interacting spin-wave calculations and direct numerical simulation, I will illustrate and validate this framework for several key models of order-by-disorder. Finally, I will discuss some implications of this picture for diagnosing order-by-disorder in numerical simulations and for candidate materials exhibiting order-by-disorder selection.
Bio: I’m an assistant professor at the University of Windsor focusing on theoretical condensed matter physics. Most of my research falls under the broad heading of quantum magnetism, with some excursions into strongly correlated systems more generally. Recently I’ve been focusing on various realizations of frustrated magnets with strong anisotropy, such as found in rare-earth and heavy transition metal magnets.
Students and postdocs are invited to stay and chat with the speaker from 11:30-12:00.
