A distinct anomaly exists within a series of iron arsenic superconductors, possibly indicating a new form of iron-based superconductivity. This is seen in plots of the temperature at which the material becomes superconducting (Tc) compared to the change in heat capacity at the superconducting temperature.(Heat capacity is the amount of heat needed to raise the temperature of a material by one degree.)Typically, newly discovered Fe-base superconductors follow a simple empirical rule:the change in the sample’s heat capacity when it becomes superconducting varies with the cube of the temperature at which the sample becomes superconducting. Researchers carefully examined high purity, single phase, polycrystalline samples of barium and potassium-containing iron arsenic superconductors of 8 different compositions ranging from x = 0.2 to x = 1.0. Below x = 0.7, Ba1-xKxFe2As2follows the same trend seen for other iron arsenic superconductors. At 0.7 the material starts to deviate from the expected results. The findings suggest that there is a significant modification in the superconducting state around x = 0.7, suggesting a new type of iron-based superconductivity. Further measurements of materials with composition around this concentration are needed to understand the cause of the anomaly.
Heat Capacity Jump at Tc and Pressure Derivatives of Superconducting Transition Temperature in the Ba1-xKxFe2As2 (0.2 ≤ x ≤ 1.0) Series