Observation of Ising spin-nematic order and its close relationship to   the superconductivity in FeSe single crystals
  Superconducting FeSe single crystals of (001) orientation are synthesized via a hydrothermal ion-release route. An Ising spin-nematic order is identified by our systematic measurements of in-plane angular-dependent magnetoresistance (AMR) and static magnetization. The turn-on temperature of anisotropic AMR signifies the Ising spin-nematic ordering temperature Tsn, below which a two-fold rotational symmetry is observed in the iron plane. A downward curvature appears below Tsn in the temperature dependence of static magnetization for the weak in-plane magnetic field as reported previously. Remarkably, we find a universal linear relationship between Tc and Tsn among various superconducting samples, indicating that the spin nematicity and the superconductivity in FeSe have a common microscopic origin. 
Yuan Dongna, Yuan Jie, Huang Yulong, Ni Shunli, Feng Zhongpei, Zhou   Huaxue, Mao Yiyuan, Jin Kui, Zhang Guangming, Dong Xia...
cond-mat.supr-con