It is thought that ultra-thin films, that is, substances that spread in two dimensions, have completely different properties from those of three-dimensional substances.For example, iron selenium (FeSe, Se is element 2), which is a superconducting substance, must be cooled to -3 ° C in the state of a three-dimensional mass to make it superconducting.On the other hand, it is known that two-dimensional, ultra-thin film FeSe becomes superconducting at -34 ° C.However, FeSe tends to deteriorate in the atmosphere, and it was very difficult to investigate the relationship between the superconducting state and the film thickness.

　Until now, FeSe ultra-thin films have been made by peeling the surface from the mass with adhesive tape.On the other hand, in the method newly developed by the group, a slightly thicker (about several tens of nanometers, 1 nanometer = 0.000000001 meters) FeSe plate is prepared first.When this is immersed in a special liquid and a voltage is applied, FeSe dissolves from the surface of the plate and becomes thinner and thinner.In the end, it can be made as thick as one atom, and it is easy to prepare a sample of any thickness.

　This makes it possible to investigate the relationship between superconductivity and film thickness in detail.It is a superconducting phenomenon that must be cooled to near absolute zero, but as research progresses, a superconducting state at a higher temperature has been realized.The mechanism of superconductivity has not been completely elucidated yet, and the dream of room temperature superconductivity is still far from being realized.However, the accumulation of such research will be a step toward the realization of the dream of room temperature superconductivity.

Source:[Tohoku University] Establishment of new ultra-thin film technology for iron-based superconductors