Fig. 2: Doping dependence of spin fluctuations for H∥a in FeSe.
a, b, The phase diagrams of Fe1−xCoxSe and FeSe1−ySy, respectively. For Co doping, Tnem is hardly influenced, but Tc is strongly suppressed. In contrast, for S doping, Tnem is suppressed with increasing y, and Tc remains nearly the same. The asterisk (*) and cross (×) symbols are the Tnem and Tc data, respectively, extracted from ref. 17. c, The spin-lattice relaxation rate divided by temperature, \({({T}_{1}T)}^{-1}\) which measures spin fluctuations, as a function of temperature and Co-doping x in Fe1−xCoxSe. The enhancement of \({({T}_{1}T)}^{-1}\) at low temperatures is progressively suppressed with increasing x (see Fig. 3). The solid lines are guides to the eyes. d, \({({T}_{1}T)}^{-1}\) as a function of temperature and S-doping y in FeSe1−ySy. Spin fluctuations are unchanged with increasing S-doping y, being consistent with Tc that is nearly independent of y.
