Zero-bias anomaly in homogeneously disordered MoGe nanowires undergoing a superconductor-insulator transition

Abstract

Nanowires made of superconducting Mo-Ge alloys undergo a superconductor-insulator transition when their cross-sectional area is reduced. On the insulating side of the transition, the differential resistance of the nanowires drops with voltage and displays a positive zero-bias anomaly (ZBA). To reveal the origin of this ZBA, we fabricated and studied a series of nanowires made of amorphous alloys with composition $\mathrm{M}{\mathrm{o}}_{50}\mathrm{G}{\mathrm{e}}_{50}$. The length of wires was in the range 150 nm--11 \ensuremath{\mu}m and width was in the range 10--20 nm. We also fabricated and measured several more complex nanowire-based structures: (i) a nanowire gated by a nearby film electrode, (ii) a nanowire connected to film electrodes with an ``adiabatically reduced'' width, (iii) a nanowire with a multielectrode configuration which allowed comparison of different sections of the same nanowire, and (iv) a nanowire with different sizes of film electrodes. We found that for $\mathrm{M}{\mathrm{o}}_{50}\mathrm{G}{\mathrm{e}}_{50}$ nanowires all experimental parameters of the ZBA and their dependence on nanowire length can be explained by electron heating. Several physical processes thought to be responsible for the ZBA have been analyzed and rejected.