Pair breaking due to orbital magnetism in iron-based superconductors

Abstract

We consider superconductivity in the presence of impurities in a two-band model suited for the description of iron-based superconductors. We analyze the effect of interband scattering processes on superconductivity, allowing for orbital, i. e., non-spin-magnetic but time-reversal-symmetry-breaking impurities. Pair-breaking in such systems is described by a nontrivial phase in an interbandscattering matrix element. We find that the transition temperature of conventional superconductors can be suppressed due to interband scattering, whereas unconventional superconductors may be unaffected. We also discuss the stability of density wave phases in the presence of impurities. As an example, we consider impurities associated with imaginary charge density waves that are of interest for iron-based superconductors.

Dirty two-band superconductivity with interband pairing order

“…The electronic structure given in equation (6) may poses both the interband and the intraband s-wave order parameters in its superconducting phase. The effects of potential disorder on T c for intraband superconductivity have been already studied theoretically in previous papers [5][6][7][8][9][10]. In our model, the amplitudes of two intraband pair potentials are expected be equal to each other because of the symmetry in the two conduction bands.…”

“…On the other hand, unconventional superconductivity such as p-and d-wave symmetry is fragile in the presence of impurities. The robustness of an s-wave Cooper pair under potential disorder, however, may be weakened in a two-band superconductor as discussed in previous literature [4][5][6][7][8][9][10]. In these papers, the intraband pairing order is assumed in each conduction band.…”

Origin of nematic order in FeSe

“…Although at present no microscopic mechanism is known to give u 2 (0) < 0 [34], this could be another possibility to explain the existence of nematic order without magnetic order in FeSe. Note also that the near-degeneracy between SDW and iCDW gives rise to nucleation of local iCDW order in the presence of pointlike impurities, which favor iCDW against SDW [44].…”

Interplay between superconductivity and itinerant magnetism in underdoped Ba1−xKxFe2As2 (x = 0.2) probed by the response to controlled point-like disorder

“…Although its response to non-magnetic scattering depends sensitively on the multi-band structure of the pairing interaction, on the chemical potential, and on the gap anisotropy, it is generally expected that inttaband scattering is much less efficient in causing pair-breaking than interband scatter-ing [7,18,[21][22][23][24][25][26][27][28]. Additionally, the orbital content of the bands can also affect the suppression of T c [23,24,[29][30][31][32]. We note that the multi-band character of the superconducting state alone is not sufficient to have T c suppression [33].…”