The material helps make small devices that change how light moves and can be used in future light-based tools and systems.
MIT researchers have developed a new nanophotonic platform using chromium sulfide bromide (CrSBr), a layered quantum material that could transform the design of modern optical devices. This enables ultracompact efficient components that can dynamically switch optical modes, something previously difficult to achieve in nanophotonics.
CrSBr’s key advantage lies in its combination of magnetic ordering and strong optical response. It allows for continuous and reversible tuning of optical properties using modest magnetic fields without mechanical movement or thermal changes. This tunability combined with a high refractive index allows the creation of optical structures just a few nanometers thick, far smaller than those made from conventional materials.
The material’s optical behavior is driven by excitons, quasiparticles formed when light excites an electron leaving behind a positively charged hole. These bound pairs interact strongly with light and are highly responsive to magnetic fields, making it possible to control how light moves through the material.
Unlike traditional nanophotonic materials such as silicon, silicon nitride, and titanium dioxide, CrSBr offers significant improvements in two key areas, refractive index and tunability. Existing materials have relatively modest refractive indices, limiting the degree to which they can confine light and thus restricting how compact devices can be. Additionally, their optical properties are fixed after fabrication, meaning any change typically requires physically altering the structure.
CrSBr overcomes both limitations. Its large refractive index allows tighter light confinement while its magnetic sensitivity enables dynamic control. When a magnetic field is applied the refractive index shifts significantly, enabling devices to switch between different optical modes without any moving parts.
This strong light-matter interaction also leads to the natural formation of polaritons, hybrid quasiparticles that combine properties of light and matter. These polaritons support enhanced nonlinear optical effects and enable quantum light transport even without external optical cavities.
So far, demonstrations have used CrSBr flakes operating at cryogenic temperatures up to 132 kelvins. However, the material is compatible with existing photonic platforms and could be used as a tunable component in future photonic circuits. This is particularly promising for applications in quantum simulation, nonlinear optics, and reconfigurable polaritonic systems where low-temperature operation is acceptable.
Research is ongoing to find related materials with higher magnetic ordering temperatures which could support room-temperature operation and broader adoption in practical devices