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

TL;DR

This study investigates two-channel Kondo effects in Al/AlO$_{x}$/Sc tunnel junctions, revealing a transition from logarithmic to square-root temperature dependence and identifying localized spin-$rac{1}{2}$ Sc atoms as the source of Kondo physics.

Contribution

It reports the first observation of two-channel Kondo behavior in planar tunnel junctions and links it to localized Sc spins at the interface.

Findings

Zero-bias conductance crosses over from -ln T to -√T dependence.

Finite bias conductance shows two-channel Kondo scaling.

Localized Sc atoms are responsible for the observed Kondo effects.

Abstract

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-$\frac12$ Sc atoms situated slightly inside the AlO$_x$/Sc interface.