Effect of nonmagnetic impurities on $s_{\pm }$ superconductivity in the presence of incipient bands

Abstract

Several Fe chalcogenide superconductors without hole pockets at the Fermi level display high temperature superconductivity, in apparent contradiction to naive spin fluctuation pairing arguments. Recently, scanning tunneling microscopy measurements have measured the influence of impurities on some of these materials, and claimed that non-magnetic impurities do not create in-gap states, leading to the conclusion that the gap must be $s_{++}$, i.e. conventional $s$ wave with no gap sign change. Here we critique this argument, and give various ways sign-changing gaps can be consistent with the absence of such bound states. In particular, we calculate the bound states for an $s_{\pm }$ system with a hole pocket below the Fermi level, and show that the nonmagnetic impurity bound state energy generically tracks the gap edge $E_{min}$ in the system, thereby rendering it unobservable. A failure to observe a bound state in the case of a nonmagnetic impurity can therefore not be used as an argument to exclude sign-changing pairing states.

6 pages, 13 figures

References in corpus (9)

• High Temperature Superconductivity in Iron Pnictides and Chalcogenides
• Common Electronic Origin of Superconductivity in (Li,Fe)OHFeSe Bulk Superconductor and Single-Layer FeSe/SrTiO3 Films
• d-wave pairing from spin fluctuations in the KxFe{2-y}Se2 superconductors
• Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunneling microscopy
• Using Gap Symmetry and Structure to Reveal the Pairing Mechanism in Fe-based Superconductors
• Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
• Fe-based superconductors: seven years later
• Electron pairing in the presence of incipient bands in iron-based superconductors
• Anomalous density of states in multiband superconductors near Lifshitz transition

Cited by in corpus (10)

• Monolayer FeSe on SrTiO${}_3$
• Surface electronic structure and evidence of plain s-wave superconductivity in (Li0.8Fe0.2)OHFeSe
• Unconventional multi-band superconductivity in bulk SrTiO${}_3$ and LaAlO${}_3$/SrTiO${}_3$ interfaces
• Using electron irradiation to probe iron - based superconductors
• Heterostructural one-unit-cell FeSe/SrTiO3: from high-temperature superconductivity to topological states
• Interplay between superconductivity and itinerant magnetism in underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ ($x=$ 0.2) probed by the response to controlled point-like disorder
• Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first order phase transition
• Impact of disorder on the superconducting transition temperature near a Lifshitz transition
• In-gap bound states induced by a single nonmagnetic impurity in sign-preserving s-wave superconductors with incipient bands
• Signatures of Amorphous Shiba State in FeTe${}_{0.55}$Se${}_{0.45}$