Eu3Bi2S4F4: uncovering mysteriously suppressed superconductivity using F–µ–F states

Cuprate superconductors have attracted considerable research interest over the past few decades due to their high transition temperatures which
allows superconductivity to be accessed at liquid nitrogen temperatures. In light of this, there has been considerable effort in finding materials with similarities to cuprates which may also exhibit superconductivity at high temperatures. One of the promising families of materials are those formed of BiS2-layers, which tend to have a crystal structure analogous to cuprates. One of the most recently discovered compounds which exhibits superconductivity is Eu3Bi2S4F4, which consists of Eu3F4 layers which crystalize into a CaF2-like structure (where the fluoride ions are in a simple cubic arrangement), sandwiching bilayers of BiS2. Polycrystalline samples of this material shows a superconducting transition below about 1.5K, but this is not present in single crystal samples. This experiment aims to find out why, by observing the way in which the F--mu--F state changes with temperature for both single crystal and polycrystalline samples.