A magnetic origin for high temperature superconductivity in iron pnictides

TL;DR

This paper demonstrates that high-temperature superconductivity in iron pnictides is driven by magnetic interactions, specifically high-energy spin excitations and their coupling to itinerant electrons, as shown through neutron scattering experiments.

Contribution

It reveals that both high-energy spin excitations and low-energy itinerant electron-spin coupling are crucial for high-Tc superconductivity in iron pnictides, providing a magnetic origin explanation.

Findings

Superconductivity correlates with low-energy itinerant electron-spin excitation coupling.

High-energy spin excitations contribute significantly to magnetic exchange energy.

Magnetic exchange energy change accounts for the superconducting condensation energy.

Abstract

In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, superconductivity occurs when electrons form coherent Cooper pairs below the superconducting transition temperature Tc. Although the kinetic energy of paired electrons increases in the superconducting state relative to the normal state, the reduction in the ion lattice energy is sufficient to give the superconducting condensation energy. For iron pnictide superconductors derived from electron or hole doping of their antiferromagnetic (AF) parent compounds, the microscopic origin for supercnductivity is unclear. Here we use neutron scattering to show that high-Tc superconductivity only occurs for iron pnictides with low-energy itinerant electron-spin excitation coupling and high energy spin excitations. Since our absolute spin susceptibility measurements for optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above Tc can account for the superconducting condensation energy, we conclude that the presence of both high-energy spin excitations giving rise to a large magnetic exchange coupling J and low-energy spin excitations coupled to the itinerant electrons is essential for high-Tc superconductivity in iron pnictides.