Born-limit scattering and pair-breaking crossover in d-wave superconductivity of (TMTSF)2ClO4

TL;DR

This study investigates how controlled disorder affects the superconducting state in (TMTSF)2ClO4, revealing a transition from strong to weak scattering and supporting d-wave pairing symmetry in this organic superconductor.

Contribution

It provides the first clear experimental identification of Born-limit pair-breaking effects and a crossover from strong to weak scattering in an unconventional superconductor.

Findings

ClO4 randomness acts as Born-limit pair breakers.

Evidence of a crossover from strong unitarity to Born-limit scattering.

Supports d-wave pairing symmetry in (TMTSF)2ClO4.

Abstract

In the quasi-one-dimensional organic unconventional superconductor (TMTSF)2ClO4, the randomness of the non-centrosymmetric ClO4 anions can be experimentally controlled by adjusting the cooling rate through the anion-ordering temperature. This feature provides a unique opportunity to study disorder effects on unconventional superconductivity in great detail. We here report on measurements of the electronic specific heat of this system, performed under various cooling rates. The evolution of the residual density of states indicates that the ClO4 randomness works as Born-limit pair breakers, which, to our knowledge, has never been clearly identified in any unconventional superconductors. Furthermore, detailed analyses suggest a peculiar crossover from strong unitarity scattering due to molecular defects toward the Born-limit weak scattering due to borders of ordered regions. This work supports the d-wave nature of pairing in (TMTSF)2ClO4 and intends to provide an experimental basis for further developments of pair-breaking theories of unconventional superconductors where multiple electron scattering mechanisms coexist.