Effect of Underlayer Induced Charge Carrier Substitution on the Superconductivity of Ti40V60 Alloy Thin Films

Abstract

The influence of metallic and semiconducting (V, Al, and Si) under-layer induced charge carrier substitution on the superconducting properties of the Ti40V60 alloy thin films are studied and also compared with a pristine reference film without any under-layer. All the films exhibit metallic behavior in the normal state and a superconducting transition at low temperatures, where the superconducting transition temperature is tunable between 4.77 K and 5.73 K. Hall measurements on the films reveal that the under-layer strongly affects the charge carrier type and density, leading to a correlation between increasing carrier concentration and decreasing TC. The Si under-layer introduces the highest disorder, yet yields the highest TC. This indicates that in the Ti40V60 alloys, a moderate amount of disorder suppresses the spin-fluctuations (inherent to the alloy system) induced pair breaking, thereby enhancing the superconductivity. The comparable TC of the film with V under-layer and the film without under-layer, and the much smaller coherence length (~6.2 nm) as compared to the film thickness (25 nm), confirm the absence of any significant proximity effects. These findings demonstrate that under-layer engineering provides an effective route to tune the superconducting properties of Ti-V alloy thin films.