Modulation of pairing symmetry with bond disorder in unconventional superconductors

Abstract

We study a two-orbital t−J1−J2 model, originally developed to describe iron-based superconductors at low energies, in the presence of bond disorder (via next-nearest-neighbor J2-bond dilution). By using the Bogoliubov–de Gennes approach, we self-consistently calculate the local pairing amplitudes and the corresponding density of states, which demonstrate a change of dominant pairing symmetry from s± wave to d wave when increasing disorder strength as long as J1≲J2. Moreover, the combined pairing interaction and strong bond disorder lead to the formation of s±-wave “islands” with length scale of the superconducting coherence length embedded in a d-wave “sea.” This picture is further complemented by the disorder-averaged pair-pair correlation functions, distinct from the case with potential disorder, where the “sea” is insulating. Due to this inevitable formation of spatial inhomogeneity, the superconducting Tc determined by the superfluid density ρs(T) obviously deviates from the value predicted by the conventional Abrikosov-Gorkov theory, where the pairing amplitudes are viewed as uniformly suppressed as the disorder increases.

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