Absence of magnetism in the superconductor Ba2Ti2Fe2As4O: Insights from inelastic neutron scattering measurements and ab initio calculations of phonon spectra

TL;DR

This study uses inelastic neutron scattering and ab initio calculations to demonstrate that Ba2Ti2Fe2As4O is a non-magnetic superconductor with no detectable magnetic effects influencing its phonon spectra.

Contribution

The paper provides experimental and theoretical evidence confirming the absence of magnetism in Ba2Ti2Fe2As4O, clarifying its unconventional superconducting nature.

Findings

No magnetic effects observed in phonon spectra

Phonon spectra well reproduced by non-magnetic calculations

Ba2Ti2Fe2As4O is confirmed as a non-magnetic superconductor

Abstract

Ba2Ti2Fe2As4O is a self-doped superconductor exhibiting a Tc ~ 21.5 K and containing, distinctively with respect to other Fe-based superconductors, not only [Fe2As2] layers but also conducting [Ti2O] sheets. This compound exhibits a transition at T* ~ 125 K which has tentatively been assigned in the literature to a possible density-wave order. However, the nature of this density wave (whether it is a charge- or spin-induced) is still under debate. Magnetism in Ba2Ti2Fe2As4O has never been experimentally confirmed, which raises the question whether this superconductor might be non-magnetic or exhibiting a very weak magnetism. Here, we report evidence from inelastic neutron scattering (INS) measurements and ab initio calculations of phonon spectra pointing towards absence of magnetism in Ba2Ti2Fe2As4O. The INS measurements did not reveal any noticeable change of the phonon spectra across Tc, neither could magnetic effects be observed within the accessible (Q, E) space, setting Ba2Ti2Fe2As4O as an unconventional superconductor. The effect of magnetism on describing phonon spectra was further investigated by performing ab initio calculations. In this context, non-magnetic calculations reproduced well the measured phonon spectra. Therefore, our results indicate a non-magnetic and unconventional character of the superconductor Ba2Ti2Fe2As4O.