Transfer of optical spectral weight in magnetically ordered superconductors

TL;DR

This paper investigates how, in antiferromagnetic superconductors, spectral weight shifts from high energies to low energies below the superconducting transition, influenced by magnetic order and spin density waves, affecting superfluid density.

Contribution

It reveals that spectral weight transfer in magnetic superconductors involves energies much larger than the superconducting gap, unlike in non-magnetic cases, and links this to magnetic order effects.

Findings

Spectral weight transfer originates from energies above 2Δ.

Superfluid condensate is enhanced by spectral weight from spin density wave gap.

Application to iron arsenides explains superfluid density reduction with magnetism.

Abstract

We show that, in antiferromagnetic superconductors, the optical spectral weight transferred to low frequencies below the superconducting transition temperature originates from energies that can be much larger than twice the superconducting gap $\Delta$. This contrasts to non-magnetic superconductors, where the optical spectrum is suppressed only for frequencies below $2\Delta$. In particular, we demonstrate that the superfluid condensate of the magnetically ordered superconductor is not only due to states of the magnetically reconstructed Fermi surface, but is enhanced by transfer of spectral weight from the mid infrared peak generated by the spin density wave gap. We apply our results to the iron arsenide superconductors, addressing the decrease of the zero-temperature superfluid density in the doping regime where magnetism coexists with unconventional superconductivity.