Energy Gap Induced by Impurity Scattering: New Phase Transition in Anisotropic Superconductors

TL;DR

This paper demonstrates that impurity scattering can induce a phase transition in layered anisotropic superconductors, changing the energy spectrum from gapless to gapped at a critical scattering rate.

Contribution

It reveals a new impurity-driven phase transition mechanism in anisotropic superconductors with sign-changing order parameters.

Findings

Superconductors undergo a phase transition regulated by impurity scattering rate.

The energy spectrum shifts from gapless to gapped at a critical scattering rate.

Impurity scattering influences the superconducting state's properties.

Abstract

It is shown that layered superconductors are subjected to a phase transition at zero temperature provided the order parameter (OP) reverses its sign on the Fermi-surface but its angular average is finite. The transition is regulated by an elastic impurity scattering rate $1/\tau$. The excitation energy spectrum, being gapless at the low level of scattering, develops a gap as soon as the scattering rate exceeds some critical value of $1/\tau_\star$.