Magnetic hour-glass dispersion and its relation to high-temperature superconductivity in iron-tuned Fe${}_{1+y}$Te${}_{0.7}$Se${}_{0.3}$

Abstract

High-temperature superconductivity remains arguably the largest outstanding enigma of condensed matter physics. The discovery of iron-based high-temperature superconductors has renewed the importance of understanding superconductivity in materials susceptible to magnetic order and fluctuations. Intriguingly they show magnetic fluctuations reminiscent of the superconducting (SC) cuprates, including a 'resonance' and an 'hour-glass' shaped dispersion, which provide an opportunity to new insight to the coupling between spin fluctuations and superconductivity. Here we report inelastic neutron scattering data on Fe${}_{1+y}$Te${}_{0.7}$Se${}_{0.3}$ using excess iron concentration to tune between a SC ($y=0.02$) and a non-SC ($y=0.05$) ground states. We find incommensurate spectra in both samples but discover that in the one that becomes SC, a constriction towards a commensurate hourglass shape develop well above $T_c$. Conversely a spin-gap and concomitant spectral weight shift happen below $T_c$. Our results imply that the hourglass shaped dispersion is most likely a pre-requisite for superconductivity, whereas the spin-gap and shift of spectral weight are consequences of superconductivity. We explain this observation by pointing out that an inwards dispersion towards the commensurate wave-vector is needed for the opening of a spin gap to lower the magnetic exchange energy and hence provide the necessary condensation energy for the SC state to emerge.

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Cited by in corpus (14)

• Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity
• Superconductivity, Antiferromagnetism, and Neutron Scattering
• The magnetic and structural properties near the Lifshitz point in Fe1+xTe
• Signatures of quantum criticality in the thermopower of Ba(Fe(1-x)Co(x))2As2
• Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity
• Soft striped magnetic fluctuations competing with superconductivity in Fe_{1+x}Te
• Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe${}_{1-x}$Se${}_x$
• Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98-zCuzTe0.5Se0.5
• Coexistence of superconductivity and short-range double-stripe spin correlations in Te-vapor annealed FeTe${}_{1-x}$Se${}_x$ with $x\le 0.2$
• Doping dependence of the spin excitations in Fe-based superconductors Fe1+yTe1-xSex
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• High-field irreversible moment reorientation in the antiferromagnet Fe${}_{1.1}$Te
• Unified Spin Model for Magnetic Excitations in Iron Chalcogenides