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Stoner Ferromagnetism in a Thermal Pseudospin-1/2 Bose Gas

Artist depiction of a Bose-Einstein condensate. Image credit, Kelley/JQI

Strongly correlated electronic systems, like superconductors, display remarkable electronic and magnetic properties. Creating analogous states in Bose gases is an excellent way to model the dynamics of these systems, offering a level of control often not possible in solid state systems.

In this PFC-supported work, theorists proposed a new magnetic phase for a Bose gas. The transition to this phase is analogous to the formation of ferromagnetism in magnetic materials, like iron, and might give insight into the physics of strongly-correlated electronic systems.

In many experiments a Bose-Einstein condensate is composed of identical particles, and will transition into a normal gas that behaves similar to air when heated. In order to uncover more interesting transitions, the theorists introduced competing terms into the system by replacing a uniform Bose gas with one composed of two different variations of an atom, spin-up and spin-down — here the spins interact differently depending on their orientation.

They then performed calculations to see which interactions would dominate while undergoing a transition. The result is a new phase diagram, illustrating the various states and transitions of the system.

These calculations were performed in three dimensions, and the researchers believe that closely examining these transitions in lower dimensions may reveal even more exotic phases. For instance, with the addition of spin to the Bose gas there is a possibility that the atoms will form bound states, like the pairing of electrons in a superconductor. In 2D, this transition happens very close to the transition to a ferromagnetic state, but a more sophisticated theory might reveal how and when the gas selects between a bound state and a magnetic one.

J. Radić, S.S. Natu, V. Galitski
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