Physics (Internal)

Metamagnets: How Do They Work?

This event is part of the Departmental Seminars.

Dissertation Committee: Anders Sandvik, Claudio Chamon, David Campbell, Robert Carey, Shyam Erramilli

Abstract:

A wide variety of physical phenomena can be studied by considering only a lattice of localized spins with short-range interactions. I present a series of large-scale studies of one such spin model—the J-Q model—conducted using the stochastic series expansion quantum Monte Carlo method. By imposing an external magnetic field, I demonstrate that J-Q model undergoes magnetization jumps to saturation above a critical coupling ratio qmin (below which the transition to saturation is continuous). These jumps are an example of metamagnetism, a type of first-order quantum phase transition. Using a high-magnetization expansion, I determine qmin exactly and show that the magnetization jumps are caused by the onset of bound states of magnons (flipped spins against a fully polarized background). I will also discuss the magnetization near saturation for q<qmin, where it obeys a zero-scale-factor universality.