  Many modern spintronic technologies, such as spin valves, spin Hall
applications, and spintronic THz emitters, are based on electrons crossing
buried internal interfaces within metallic nanostructures. However, the complex
current pathways within such nanostructures are difficult to disentangle using
conventional experimental methods. Here, we measure the conductivity of a
technologically relevant Ru/Co bilayer nanostructure in a contact-free fashion
using THz time-domain spectroscopy. By applying an effective resistor network
to the data, we resolve the complex current pathways within the nanostructure
and determine the degree of electronic transparency of the internal interface
between the Ru and Co nanolayers.
