Switching of intra-orbital spin excitations in electron-doped iron pnictide superconductors

TL;DR

This study explores how intra-orbital spin excitations in electron-doped iron pnictide superconductors change with doping, revealing a switch in dominant orbital contributions that correlates with superconducting properties.

Contribution

It demonstrates the doping-dependent switching of intra-orbital spin excitations and highlights the importance of multi-orbital effects in superconductivity of iron pnictides.

Findings

Spin fluctuations appear around x=0.1 and 0.4, vanish at x=0.2.

The switching of intra-orbital nestings explains the doping dependence.

Multi-orbital effects are crucial for understanding Tc variations.

Abstract

We investigate the doping dependence of the magnetic excitations in two-superconducting-dome-system LaFeAsO1-xDx. Using inelastic neutron scattering, spin fluctuations at different wavenumbers were observed under both superconducting domes around x = 0.1 and 0.4, but vanished at x = 0.2 corresponding to the Tc valley. Theoretical calculations indicate that the characteristic doping dependence of spin fluctuations is rationally explained as a consequence of the switching of the two intra-orbital nestings within Fe-3dYZ, ZX and 3dX2-Y2 by electron doping. The present results imply that the multi-orbital nature plays an important role in the doping and / or material dependence of the Tc of the iron pnictide superconductors.