What they found was surprising: instead of having one energy level, the excitons split into two distinct energy levels—a phenomenon known as fine structure. It was also observed that excitons behaved differently depending on which direction they moved in the material.
For instance, at very cold temperatures (below -222°F or 132 Kelvin), CrSBr becomes magnetic. So, inside each of its layers, the tiny magnetic fields of the electrons line up, but in opposite directions from one layer to the next. This is called an antiferromagnetic state. Here, excitons are found to be trapped inside a single layer, moving only in one direction.
However, at warmer temperatures (above 132 Kelvin), CrSBr loses its magnetism, and the heat makes the electron spins point in random directions. In this case, excitons are no longer confined. They spread out over multiple layers and move freely in all directions, showing three-dimensional behavior.