Superconductivity, in particular high temperature superconductivity, has attracted great interest from both physicists and material scientists over a century or so. This is because superconductivity is an outstanding quantum phenomenon that contains enormously rich physics and it has a great perspective of industry application. Currently, there are two family members of high temperature superconductors. One is copper oxides, and the other is iron pnictides. They share one common aspect. Namely, high temperature superconductivity occurs in the vicinity of antiferromagnetism. Therefore, it has been believed by many that magnetic fluctuations associated with the nearby magnetism are responsible for high temperature superconductivity.

Recently, scientists in Institute of Physics, Chinese Academy of Sciences, discovered a new phase of high temperature superconductivity in an iron-pnictide material that is far from magnetism. The superconducting transition temperature Tc is even higher than its counterpart near a magnetic ordered phase, reaching to 41 K (defined by resistivity).

In 2008, the iron-pnictide compound LaFeAsO1-xFx was discovered by Prof. Hosono’s group (Tokyo Institute of Technology, Japan) to be superconducting with a maximal Tc =26. This was achieved by replacing O with F in a magnet LaFeAsO, but the F-content (x) cannot exceed 0.2 and strong magnetic fluctuations survive. By the high-pressure synthesis technique, Dr. Jie Yang in Prof. Guo-qing Zheng’s group, collaborating with Prof. Z.X. Zhao and Prof. J.Q. Li, succeeded in making high-content of fluorine (0.75>x>0.25), and discovered a new superconducting dome that is far away from a magnetic ordered phase. Instead of magnetism or magnetic fluctuations, they found a nematic structural transition above the new superconducting dome. They have also succeeded in probing the quantum fluctuations associated with the nematic phase transition, which is responsible for the formation of the new dome.

This work has the following impacts. First, the work suggests that, in addition to the conventional phonon or magnetic fluctuations mechanisms, there is a new route to high temperature superconductivity. Secondly, the work also sheds light on the physics of another class of materials called heavy fermion materials where two superconducting phases were reported previously.

This study entitled “New Superconductivity Dome in LaFeAsO1−xFx Accompanied by Structural Transition” was published on Chinese Physics Letters　(Chin. Phys. Lett. 32, 107401 (2015)).

The study was supported by the National Science Foundation of China, the Ministry of Science and Technology of China, and by Chinese Academy of Sciences.