A research team, including members from the University of Tokyo, systematically substituted one atom for another in an iron-based superconductor and discovered a new critical point (singularity) at which the electronic state of the superconductor changes drastically. This singularity is completely different to conventional singularities and may indicate a new mechanism for achieving superconductivity.
Studies on singularities offer important clues for understanding various physical phenomena, just as black holes, which are a kind of singularity, can shed light on the origin of the universe. Research on superconductors – which deals with superconductivity, or the phenomenon in which electricity transmission is achieved without loss of thermal energy – in theory suggests that anomalous electronic states emerging near these critical points serve as the source for inducing superconductivity. While magnetic critical points have previously been found in iron-based superconductors, whether a new singularity without magnetic properties existed remained unclear.
Drawing on the fact that electrons exhibit liquid crystal properties, the research team, including graduate student Suguru Hosoi and Professor Takasada Shibauchi, Department of Advanced Materials Science, School of Frontier Sciences, University of Tokyo, focused on iron selenide (FeSe), a superconductor that does not express magnetic properties, to study the effect of substituting some selenium atoms with those of sulfur (FeSe1-xSx), which have a smaller atomic radius. From this research, the team found that substituting approximately 17 percent of the selenium atoms with sulfur atoms led to the discovery of a new singularity that lacked magnetism.
By demonstrating that a new mechanism of superconductivity can be achieved through uncovering the relationship between this new singularity and superconductivity, researchers anticipate the opening of a new path toward realizing superconductivity at higher temperatures.
“In conventional superconductivity in simple metals, usually high temperature superconductivity is not realized. To produce superconductivity at higher temperatures, it is important to verify other mechanisms of superconductivity,” says Shibauchi. He continues, “The present finding of a new singular point implies the possibility of a novel liquid crystal-like origin for superconductivity, which is an important step toward the realization of a previously unexplored type of superconductivity.”