Vacuum in optical cavity can change material's magnetic state without laser excitation

The first theoretical proof that an atomically thin material, α-RuCl3, may be controlled only by inserting it into an optical cavity has been generated by researchers in the U.S. and Germany. Crucially, the material's magnetic order can be converted from a zigzag antiferromagnet to a ferromagnet only by the cavity vacuum fluctuations. The publication of the team's work may be found in npj Computational Materials.

Using strong laser light to change the characteristics of magnetic materials has become a popular issue in material physics study recently. Through careful manipulation of the laser light's characteristics, scientists have significantly altered the electrical conductivity and optical characteristics of several materials.

However, this comes with several practical issues, chief among them being the difficulty of stopping the material from heating up, and necessitates constant stimulation by high-intensity lasers. So, instead of utilizing powerful lasers, researchers are searching for ways to use light to influence materials in a similar way.

Theorists at the University of Pennsylvania, Stanford University, and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg, Germany have now developed a radically new method for altering a real material's magnetic properties in a cavity without the use of laser light. Their cooperation demonstrates that the zigzag antiferromagnet α-RuCl3 may become a ferromagnet just by virtue of the cavity.

Most importantly, the group shows that α-RuCl3 recognizes changes in the electromagnetic environment and modifies its magnetic state appropriately, even in a seemingly dark hollow. This effect is solely of a quantum mechanical nature, stemming from the fact that the vacuum state, also known as the empty cavity, is never truly empty in quantum theory. Rather, the light field varies, causing light particles to appear and disappear, which in turn modifies the material's characteristics.

Lead author Emil Viñas Boström, a postdoctoral researcher in the MPSD Theory Group, says, "The optical cavity confines the electromagnetic field to a very small volume, thereby enhancing the effective coupling between the light and the material." "Our results show that carefully engineering the vacuum fluctuations of the cavity electric field can lead to drastic changes in a material's magnetic properties." Since there is no requirement for light excitation, the method theoretically avoids the issues related to continuous laser driving.

This work, which builds on earlier studies into cavity control of ferroelectric and superconducting materials, is the first to demonstrate such control over magnetism in a genuine material. By creating precise chambers, the scientists aim to better comprehend the complex interactions between light and matter and reveal previously undiscovered phases of matter.