Consequences of extended $s_\pm$-wave pairing in iron-based superconductors

TL;DR

This paper investigates the effects of extended $s_ pmp$-wave pairing symmetry on the spin and charge dynamics, as well as point-contact spectroscopy, in iron-based superconductors, highlighting potential experimental signatures of nodal gaps.

Contribution

It provides a theoretical analysis of how extended $s_ pmp$-wave pairing influences observable properties, aiding in identifying pairing symmetry in iron-based superconductors.

Findings

Strong peaks in susceptibilities at specific momenta due to nesting effects.

V-shaped differential conductance indicating gap nodes in PCARS.

Distinct features in spin and charge responses linked to pairing symmetry.

Abstract

Motivated by a recent experiment of Song \emph{et al.} [Science {\bf 332}, 1410 (2011)], we theoretically study the spin dynamics, charge dynamics, and point-contact Andreev-reflection spectroscopy (PCARS) of two-band iron-based superconductors of a possible extended $s_\pm$-wave pairing symmetry. We consider the case of a dominant $s_\pm$ gap blended by a secondary extended $s$ component in which gap nodes can develop in the Fermi pockets near zone corner and/or boundary. Due to the strong nesting effect associated with nodal regions, dynamical spin and charge susceptibilities can exhibit strong peaks at momenta near $(\pm\pi/2,0)$, $(\pm\pi,\pm\pi/2)$, as well as $(\pm\pi,0)$ in the unfolded Brillouin zone. For PCARS, considering an anisotropic band effect induced by an applied voltage, [100] differential conductance can exhibit a $V$-shape behavior manifesting a gap node occurring in such direction. It is highly suggested that the above features can be experimentally investigated to help sorting out the pairing symmetry of iron-based superconductors.