This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team wanted to better understand how the forces between particles inside a material change. They discovered that by confining one-dimensional classical spin chains inside a mirror box cavity with light, they could force these magnetic particles to organize and undergo a phase transition.
Their work provides the simplest exactly solvable examples showing that light can create new phase transitions with materials. In 1925, Ernst Ising showed that a single one-dimensional chain of small magnetic particles with nearest-neighbor interactions does not exhibit a magnetic phase transition at finite temperatures. This is called the Ising chain.
However, scientists today know that magnetic phase transitions can occur in two or more dimensions, positioning the Ising model as a simple, crucial math tool for studying how large groups of interacting particles behave. In addition, scientists are using cavity systems where matter and light are trapped and strongly interact with each other, leading to the possible discovery of new phenomena in physics. In the last decade, the ultra-strong coupling of light-matter has moved from theoretical concepts to a variety of experimental systems.
These experimental systems include phonons, intersubband transitions in semiconductor quantum wells, superconducting circuits, organic molecules, electron cyclotron motion and magnons. This progress has shown scientists potential applications in both physics and chemistry. Scientists have had a special interest in observing the superradiant phase transition, which is the spontaneous buildup of a coherent electromagnetic field under thermal equilibrium due to light-matter coupling.
In their research published in the journal Physical Review Research, the research team pursued a minimal interacting route, investigating an exactly solvable cavity-coupled 1D classical model. A superradiant phase transition occurs, providing the team with the simplest solvable interacting 1D example. The construction they chose makes the mechanism explicit, showing how photon-mediated fully connected coupling, along with intrinsic interactions, produces superradiance at a specific temperature.
The classical spin model allowed the researchers to determine the finite-temperature superradiant phase transition exactly in the thermodynamic limit. Other recent studies conducted on cavity-coupled 1D systems have focused on the behavior at absolute zero temperature, while in this study, the research team explored the exact properties at finite temperatures. "We wanted to understand how interactions inside matter affect a superradiant phase transition at thermal equilibrium," said Motoaki Bamba, an associate professor at Yokohama National University's Faculty of Engineering.
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