"Superconductivity" is a phenomenon in which electrical resistance becomes zero when a specific substance is cooled to near absolute zero (0 Kelvin [K] = -273.15 ° C).In recent years, high-temperature superconductors that become superconducting at high temperatures (around -200 ° C) have been found.Among them, iron selenium has peculiar physical properties among iron-based superconductors, and in particular, it was recently discovered that the superconducting transition temperature rises more than four times by applying pressure, which is a big mystery of condensed matter physics. It was one of.

　This time, the research group applied high pressure to single crystal iron selenium to track changes in electrical resistance, and measured the temperature at which magnetism develops and the superconducting transition temperature.As a result, magnetism suddenly appears at around 2 atm, the magnetic expression temperature rises as the pressure rises to around 2 to 4 atm, falls at 4 to 6 atm, and disappears at around 6 atm.On the other hand, the superconducting transition temperature rises with the pressure rise from normal pressure to around 2 atm, but does not rise so much to around 4 atm after the appearance of magnetism, and at 4 to 6 atm, it is the opposite of the fall in magnetic manifestation temperature. It rises sharply to 6K, which is four times the normal pressure of 9K at around 4 atm.When the pressure was further increased, the superconducting transition temperature decreased, and the disappearance of superconductivity was observed.

　From this, it became clear that magnetism and superconductivity are in a competitive relationship, and that suppression of magnetism is the key to realizing high-temperature superconductivity.This research is said to be a major step toward understanding the mechanism of high-temperature superconductivity and realizing superconductivity near room temperature.