Extension of the Kibble-Zurek Mechanism

June 11, 2024& lead Physics 17, s61

A theory first applied to phase transitions in the early Universe and then to defects in superfluid helium can now account for a wider variety of systems.

In 1985 Wojciech Zurek analyzed what happens when liquid helium rapidly changes to its superfluid state. Spontaneous symmetry breaking, he predicted, would cause the superfluid to flow with a measurable, randomly directed velocity. The superfluid transition is second order, that is, gradual. Now Zurek and Fumika Suzuki—both of Los Alamos National Laboratory in New Mexico—have extended the 1985 analysis to also accommodate first-order, unexpected transitions. [1]. The extension presents the exploration of diverse and exotic phenomena in materials science, high energy physics, and cosmology.

Zurek was originally inspired by Tom Kibble, who in 1976 examined what happens when the fields permeating the infant Universe spontaneously break symmetry. As the Universe cools, regions separated by more than the distance light can travel after the Big Bang acquire different field values. Domain walls, magnetic monopoles, and other topological defects can form where different choices of broken symmetry meet. Zurek realized that, while symmetry breaking occurs at every phase transition, its universal nature can be used to calculate the defect density in any system that undergoes the same type of fast, non-equilibrium quenching. Their joint theory became known as the Kibble-Zurek mechanism (KZM).

To extend KZM to first-order transitions, Zurek and Suzuki investigated what happens when the nature of a transition can be tuned between second- and first-order. In a system that is first-order weak, as the critical point is passed, parts of the system enter the new phase, while other parts retain the advance phase. The fluctuations initiate second-order transitions and are also responsible for nucleation, which occurs in first-order transitions. By focusing on the role of fluctuations, Zurek and Suzuki figured out how to modify the KZM, enabling the prediction of the defect density across the spectrum of the first-to-second order phase transition.

– Charles Day

Charles Day is a senior editor for Journal of Physics.