Interstitial Iron Controlled Superconductivity in Fe1+xTe0.7Se0.3

TL;DR

This study demonstrates that removing interstitial iron from Fe1+xTe0.7Se0.3 enhances its superconductivity, revealing the competing roles of different iron sites and their impact on the material's magnetic and structural properties.

Contribution

It shows that topotactic deintercalation of interstitial iron can improve superconductivity in Fe(Te,Se) compounds, highlighting the importance of iron site occupancy.

Findings

Superconductivity is enhanced by removing interstitial iron.

Structural changes include flattening of Fe(Te,Se)4 tetrahedron.

Magnetic excitations evolve with iron content.

Abstract

The superconducting series, Fe(Te,Se), has a complex structural and magnetic phase diagram that is dependent on composition and occupancy of a secondary interstitial Fe site. In this letter, we show that superconductivity in Fe1+xTe0.7Se0.3 can be enhanced by topotactic deintercalation of the interstitial iron, demonstrating the competing roles of the two iron sites. Neutron diffraction reveals a flattening of the Fe(Te,Se)4 tetrahedron on Fe removal of iron and an increase in negative thermal expansion within the ab plane that correlates with increased lattice strain. Inelastic neutron scattering shows that a gapped excitation at 6 meV, evolves into gapless paramagnetic scattering with increasing iron; similar to the fluctuations observed for non-superconducting Fe1+xTe itself.