Materials with a layered structure have been the subject of great interest as potential candidates for high-temperature superconductors. The ACa2Fe4As4F2 family of materials crystallise in a body-centred tetragonal lattice containing asymmetric double layers of Fe2As2 separated by insulating CaF2 layers. This experiment will provide a detailed investigation of the effect of structural changes on the superfluid stiffness in this family of materials as the cation A is varied. It will also examine the relationship between superconductivity and the F–μ–F state that we think is likely to occur in these materials.