High-pressure NMR Study of Magnetism and Superconductivity on FeSe Single Crystals

Bulk FeSe has a structure transition at $T\sim$ 91 K and a superconducting transition at $T\sim$ 9.3 K, but no magnetic ordering at the ambient pressure. With increasing pressure, the structure transition is suppressed, whereas a magnetic ordering emerges. This is in contrast to most iron arsenides, where the structure transition is usually accompanied by a stripe magnetic ordering. Here we report our high-pressure NMR study on high-quality FeSe single crystals. The spin fluctuations and the magnetic ordering observed by our measurements give fresh information for understanding the interplay among the structure transition, the superconductivity and the magnetism in bulk FeSe materials.