In copper oxide, when holes or electron carriers responsible for electrical conduction are injected into an antiferromagnetic insulator material, the antiferromagnetic order is broken and superconductivity is developed.Since antiferromagnetic fluctuations have been observed in substances that exhibit superconductivity, it is said that antiferromagnetic fluctuations are deeply involved in the mechanism of superconductivity.
On the other hand, when a large amount of carriers are injected, superconductivity disappears, but the cause is unknown, and it is unclear what the magnetic state is with the substance injected with a large amount of carriers.

　This time, a research group led by Sophia University and Tohoku University observed two-dimensional ferromagnetic fluctuations for the first time in the world with a copper oxide injected with a large amount of holes.This means that the magnetic state changes from antiferromagnetism to ferromagnetism with the injection of carriers.In addition, since ferromagnetic fluctuations were observed in substances in which superconductivity was greatly suppressed, it is possible that ferromagnetic fluctuations are inhibiting high-temperature superconductivity, which has been a mystery for a long time. It can be said that the cause of the disappearance of superconductivity when injected can be clarified.

　From this result, it became clear that a two-dimensional ferromagnetic fluctuation state appears when a large amount of holes are injected in a copper oxide whose existence of antiferromagnetic state and superconducting state has been known so far. It was suggested that ferromagnetic fluctuations may be involved in superconductivity.It is expected to show a new way for research on high-temperature superconductivity in the future.

Paper information:[Physical Review Letters] Development of Ferromagnetic Fluctuations in Heavily Overdoped (Bi, Pb) 2Sr2CuO6 + δ Copper Oxides