Magnetic-Field-Induced Spin Nematicity in FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)Superconductor Systems

The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures under fields up to 9 T.A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR,and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn.This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)systems,no matter whether the sample shows an electronic nematic order at T_(s)≤T_(sn),or an antiferromagnetic order at TN<T_(sn),or neither order.Importantly,we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity:The spin-nematic T_(sn)is not suppressed but even enhanced by the substitution,whereas the electronicnematic T_(s)is rapidly suppressed,in the FeSe_(1-x)S_(x)system.Furthermore,we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)samples.