Two-Channel Kondo Effects in Al/AlO${}_x$/Sc Planar Tunnel Junctions

We have measured the differential conductances $G(V,T)$ in several Al/AlO${}_x$/Sc planar tunnel junctions between 2 and 35 K. As the temperature decreases to $\sim$ 16 K, the zero-bias conductance $G(0,T)$ crosses over from a standard $-$ln$T$ dependence to a novel $-\sqrt{T}$ dependence. Correspondingly, the finite bias conductance $G(V,T)$ reveals a two-channel Kondo scaling behavior between $\sim$ 4 and 16 K. The observed two-channel Kondo physics is ascribed to originating from a few localized spin-$\frac{1}{2}$ Sc atoms situated slightly inside the AlO${}_x$/Sc interface.