Magnetic-Field-Induced Crossover to a Nonuniversal Regime in a Kondo Dot

Abstract

We have measured the magnetic splitting, $Δ_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $Δ_K$ with $T_K$ along the two paths have opposite signs, indicating that $Δ_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $Δ_K$ with $T_K$ along both paths, in agreement with theoretical predictions. Furthermore, we find $Δ_K/Δ<1$ at low $B$ and $Δ_K/Δ>1$ at high $B$, where $Δ$ is the Zeeman energy of the bare spin, in the same system.

12 pages, 5 figures