Sensitivity of superconducting states to the impurity location in layered materials

Abstract

The family of multi-layered superconductors derived from the doped topological insulator Bi2Se3 has been found to be unusually robust against non-magnetic disorder. Recent experimental studies have highlighted the fact that the location of impurities could play a critical role for this puzzling robustness. Here we investigate the effects of four different types of impurities, on-site, interstitial, intercalated and polar, on the superconducting critical temperature. We find that different components of the scattering potential are active depending on the impurity configuration and choice of orbitals for the effective low-energy description of the normal state. For the specific case of Bi2Se3based superconductors, we find that only the symmetric share of impurity configurations contribute to scattering, such that polar impurities are completely inactive. We also find that a more dominant mass-imbalance term in the normal-state Hamiltonian can make the superconducting state more robust to intercalated impurities, in contrast to the case of on-site or interstitial impurities.

Nonunitary superconductivity in complex quantum materials

“…Before starting the discussion on nonunitary superconductivity, it is useful to introduce the concept of superconducting fitness [49,50], as this is going to be a key ingredient in the analysis that follows. The superconducting fitness framework has been a useful theoretical tool allowing for the understanding of the stability and nodal structure of unexpected superconducting states [8,[51][52][53], the robustness of unconventional superconducting states in the presence of impurities [4,54], and the unusual behavior of complex superconductors under external symmetry breaking fields, such as strain [55]. This seems to be one of the most appropriate frameworks for the description of superconductivity in complex quantum materials, allowing for the understanding of apparently contradicting responses of complex superconductors.…”

Nonunitary Superconductivity in Complex Quantum Materials

“…Before staring the discussion on nonunitary superconductivity, it is useful to introduce the concept of superconducting fitness [31,32], as this is going to be a key ingredient in the analysis that follows. The superconducting fitness framework has been a useful theoretical tool allowing for the understanding of the stability and nodal structure of unexpected superconducting states [33,34,35,36], the robustness of unconventional superconducting states in the presence of impurities [4,37], and the unusual behaviour of complex superconductors under external symmetry breaking fields, such as strain [38]. This seems to be one of the most appropriate frameworks for the description of superconductivity in complex quantum materials, allowing for the understanding of apparently contradicting responses of complex superconductors.…”

Impurity-induced excitations in twisted topological van der Waals superconductors

“…The gap is measured in units of the topological gap for the topological pristine system ∆ T . In particular, it is observed that the location of the impurity strongly impacts the gap of the system 87 . The resulting gap of the defective system can range from the pristine value, observed for impurities at the exchange maximum, to nearly zero, observed for impurities away from the exchange maximum (Fig.…”