Resonance as a probe of the electron superconducting gap in BaFe1.9Ni0.1As2

TL;DR

This study demonstrates that the magnetic resonance in BaFe1.9Ni0.1As2 superconductors is directly linked to the superconducting gap energy, supporting the idea that spin fluctuations play a key role in the pairing mechanism.

Contribution

It provides direct experimental evidence connecting the magnetic resonance to the superconducting gap energy in iron arsenide superconductors.

Findings

Magnetic resonance energy decreases with suppressed superconductivity

Resonance intensity correlates with superconducting gap energy

Results support spin fluctuations as a pairing mechanism

Abstract

The discovery of high-transition temperature (high-Tc) superconductivity near antiferromagnetism in iron arsenides raised the possibility of an unconventional superconducting mechansim1-8. The observation of clear Fermi surfaces and nodeless superconducting gaps by angle resolved photoemission9-12 suggests that electron pairing in these materials may be mediated by quasiparticle excitations between sign reversed hole and electron Fermi pockets5-8. Although the presence of a 'resonance' in the spin excitation spectrum found by inelastic neutron scattering13-17 is consistent with this picture18-20, there has been no direct evidence connecting the resonance to the superconducting gap energy. Here we show that for the optimally electron doped BaFe1.9Ni0.1As2 (Tc =20 K, Fig. 1c) iron arsenide superconductor, application of a magnetic field that suppresses the superconductivity and superconducting gap energy also reduces the intensity and energy of the resonance. These results suggest that the energy of the resonance is proportional to the electron pairing energy, and thus indicate that spin fluctuations are intimately related to the mechanism of superconductivity in iron arsenides.