Local Electronic Structure around a Single Impurity as a Test of Pairing Symmetry in (K,Tl)Fe${}_x$Se${}_2$ Superconductors

Abstract

We have studied the effect of a single nonmagnetic impurity in the recently discovered (K,Tl)Fe${}_x$Se${}_2$ superconductors, within both a toy two-band model and a more realistic five-band model. We have found that, out of five types of pairing symmetry under consideration, only the $d_{x^2-y^2}$-wave pairing gives rise to impurity resonance states. The intra-gap states have energies far away from the Fermi energy. The existence of these intra-gap states is robust against the presence or absence of inter-band scattering. However, the inter-band scattering does tune the relative distribution of local density of states at the resonance states. All these features can readily be accessed by STM experiments, and are proposed as a means to test pairing symmetry of the new superconductors.

4+ pages, 4 eps figures, revised version. To appear in Physical Review Letters

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• Phase diagram of doped BaFe${}_2$As${}_2$ superconductor under broken $C_4$ symmetry
• On the role of chalcogen vapor annealing in inducing bulk superconductivity in Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$
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• Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry
• Low-energy bound states at interfaces between superconducting and block antiferromagnet regions in KxFe{2-y}Se2
• A minimum single-band model for low-energy excitations in superconducting K${}_x$Fe${}_2$Se${}_2$
• Fermi surface evolution and checker-board block-spin antiferromagnetism in $A_x$Fe${}_{2-y}$Se${}_2$
• In-gap bound states induced by a single nonmagnetic impurity in sign-preserving s-wave superconductors with incipient bands
• Quasiparticle Scattering Interference in (K,Tl)FexSe2 Superconductors
• Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors