From (π,0) magnetic order to superconductivity with (π,π) magnetic resonance in Fe1.02Te1−xSex

The simplest iron-based superconductor is the chalcogenide Fe 1+ y Te 1− x Se x . Previous work suggested a different magnetic origin of superconductivity owing to differences in its electronic states of this material and the iron pnictides, or at least in their parent compounds —the undoped and non-superconducting versions. The differences are now reconciled by showing a modification of the Fe 1+ y Te 1− x Se x states when the Se content is increased. The iron chalcogenide Fe 1+ y (Te 1− x Se x ) is structurally the simplest of the Fe-based superconductors 1 , 2 , 3 . Although the Fermi surface is similar to iron pnictides 4 , 5 , the parent compoundFe 1+ y Te exhibits antiferromagnetic order with an in-plane magnetic wave vector (π,0) (ref. 6 ). This contrasts the pnictide parent compounds where the magnetic order has an in-plane magnetic wave vector (π,π) that connects hole and electron parts of the Fermi surface 7 , 8 . Despite these differences, both the pnictide and chalcogenide Fe superconductors exhibit a superconducting spin resonance around (π,π) (refs 9 , 10 , 11 ). A central question in this burgeoning field is therefore how (π,π) superconductivity can emerge from a (π,0) magnetic instability 12 . Here, we report that the magnetic soft mode evolving from the (π,0)-type magnetic long-range order is associated with weak charge carrier localization. Bulk superconductivity occurs as magnetic correlations at (π,0) are suppressed and the mode at (π, π) becomes dominant for x >0.29. Our results suggest a common magnetic origin for superconductivity in iron chalcogenide and pnictide superconductors.