Superconductor-insulator transition in quasi-one-dimensional nanowires

Abstract

We have studied a large group of superconducting MoGe nanowires fabricated by a molecular templating technique. A well-defined superconductor-insulator transition (SIT) is observed in homogeneous wires with lengths less than ~200 nm. The total normal state resistance of the wire is found to be the control parameter for this transition with the critical point occurring near the quantum of resistance for Cooper pairs. Wires in the superconducting phase of the SIT are well described by the Langer-Ambegaokar-McCumber-Halperin theory of thermally activated phase slips. No resistance “tails” characteristic of quantum phase slips were observed. Wires in the insulating phase of the SIT follow the predictions of the theory of weak Coulomb blockade in a diffusive normal metal. Longer wires display signs of a “mixed” behavior that is similar to that found for inhomogeneous wires in which a single wire acts as a combination of two or more superconducting and/or insulating sections.