Experimental validation of the interfacial form of the Wiedemann-Franz law

The thermal conductivity of four Pd/Ir metal multilayers of total thickness 390 nm with 40, 80, 120, and 200 Pd/Ir interfaces are measured at temperatures between 78 and 295 K using time-domain thermoreflectance. The thermal interface conductance G of the Pd/Ir interface is derived from the differences in thermal conductivity between the multilayers. A comparison of G to previously reported data for the electronic specific resistance of the Pd/Ir interface at 4 K supports the validity of the interfacial form of the Wiedemann-Franz law. The Lorenz number deduced from this comparison is within 10% of the Sommerfeld value at all temperatures, well within the experimental uncertainties of ≈ 20%.