Impurity-Induced In-Gap States as Probes of Sign-Changing Superconducting Order Parameters
Students learn how a single non-magnetic impurity in an unconventional superconductor generates bound or resonant electronic states inside the energy gap, and how the presence, energy, and spectral weight of those states diagnose whether the superconducting order parameter changes sign. The framework distinguishes intralayer d-wave pairing, whose sign reversal along the Fermi surface produces a mid-gap resonance, from interlayer s-wave pairing, whose sign structure yields pronounced in-gap peaks, giving impurity spectroscopy as a tool to determine pairing symmetry.
Probing Sign-Changing Order Parameters via Impurity States in unconventional superconductors
This paper uses the T-matrix method for single-impurity scattering to establish how impurity-induced electronic states in unconventional superconductors reveal the sign structure of the superconducti…