The effect of morphology on the superconductor-insulator transition in 1-D nanowires

TL;DR

This study investigates how the morphology of 1-D superconducting nanowires influences the superconductor-insulator transition, revealing that homogeneity leads to a clear transition near a specific resistance, while inhomogeneity causes mixed behaviors.

Contribution

It demonstrates that wire homogeneity determines the nature of the superconductor-insulator transition, highlighting the role of weak link constrictions in inhomogeneous wires.

Findings

Homogeneous wires show a sharp SIT near resistance h/4e^2.

Inhomogeneous wires exhibit multiple steps and mixed superconducting and insulating behaviors.

Weak link constrictions cause multiple resistance steps and differential resistance peaks.

Abstract

We study the effect of morphology on the low temperature behavior of superconducting nanowires of length $\approx$100 nm. A well-defined superconductor-insulator transition (SIT) is observed only in homogenous wires, in which case the transition occurs when the normal resistance is close to $h/4e^2$. Inhomogeneous wires, on the other hand, exhibit a mixed behavior, such that signatures of the superconducting and insulating regimes can be observed in the same sample. The resistance versus temperature curves of inhomogeneous wires show multiple steps, each corresponding to a weak link constriction (WLC) present in the wire. Similarly, each WLC generates a differential resistance peak when the bias current reaches the critical current of the WLC. Due to the presence of WLCs an inhomogeneous wire splits into a sequence of weakly interacting segments where each segment can act as a superconductor or as an insulator. Thus the entire wire then shows a mixed behavior.