At the verge of ionicity and metallicity

Superconductivity is the property of certain materials to conduct electricity without energy losses. This property appears when the material is cooled below the critical temperature. In almost all materials the critical temperature is rather low, of only a few kelvins or less. There are only two existing classes of materials, cuprates and iron-pnictides, that superconduct at temperatures of several tens of kelvins. The transition temperature record is still held by cuprates, which have demonstrated superconductivity at temperatures as high as 138 K, which is almost halfway to room temperature. We call these two classes of materials high-temperature superconductors. Despite enormous effort over three decades, the mechanism of their superconductivity is still a mystery. Achieving its understanding is really essential as it could transform the way how we use this phenomenon in applications, e.g., in novel electronics or transport. Its solution could also have a big impact in the fight against climate change. One way to make progress in understanding such materials is by discovering and studying novel and similar materials. Murunskite perfectly fit into this strategy. It is a sulfosalt which resembles to both types of materials, both in term of its electronical properties and atomic structure. The conditio sine qua non of any study of a functional material is to master the compounds crystal growth, since without a high-quality sample it is not possible to conduct research of the complex- electronic properties of the material. In the case of murunskite, we have recently achieved this milestone by synthesizing large high-quality single crystals for the first time. This way, we have established that murunskite are structurally identical to pnictides, and electronically analogous to the cuprate parent compounds. Now, our main goal is to understand the pathways that lead to the metallization of this material, since only metallic compounds can superconduct. By carefully varying the chemical composition of the murunskite parent compound, we will further develop this family of materials, characterize their properties and select those that are promising for further investigation and, perhaps could be tuned for application one day.