Crossover from impurity-controlled to granular superconductivity in (TMTSF)2ClO4

TL;DR

This study investigates how increasing disorder in (TMTSF)2ClO4 causes a transition from homogeneous d-wave superconductivity to a granular form, with implications for understanding unconventional pairing and superconducting network formation.

Contribution

It demonstrates a controllable crossover from defect-controlled to granular superconductivity in (TMTSF)2ClO4 by varying cooling rates, revealing new insights into disorder effects on pairing symmetry.

Findings

Confirmation of non-s-wave pairing via Abrikosov-Gorkov theory at slow cooling rates.

Observation of a granular superconducting network at fast cooling rates.

Identification of a disorder-driven crossover between two superconducting regimes.

Abstract

Using a proper cooling procedure, a controllable amount of non-magnetic structural disorder can be introduced at low temperature in (TMTSF)2ClO4. Here we performed simultaneous measurements of transport and magnetic properties of (TMTSF)2ClO4 in its normal and superconducting states, while finely covering three orders of magnitude of the cooling rate around the anion ordering temperature. Our result reveals, with increasing density of disorder, the existence of a crossover between homogeneous defect-controlled d-wave superconductivity and granular superconductivity. At slow cooling rates, with small amount of disorder, the evolution of superconducting properties is well described with the Abrikosov-Gorkov theory, providing further confirmation of non-s-wave pairing in this compound. In contrast, at fast cooling rates, zero resistance and diamagnetic shielding are achieved through a randomly distributed network of superconducting puddles embedded in an normal conducting background and interconnected by proximity effect coupling. The temperature dependence of the AC complex susceptibility reveals features typical for a network of granular superconductors. This makes (TMTSF)2ClO4 a model system for granular superconductivity where the grain size and their concentration are tunable within the same sample.