A magnetic field-induced crossover to a non-universal regime in a Kondo dot

We have measured the magnetic splitting, $\Delta_K$, 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 $\Delta_K$ with $T_K$ along the two paths have opposite signs, suggesting that $\Delta_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $\Delta_K$ with $T_K$ along both paths. Detailed $\Delta_K(B)$ data for two different $T_K$ show consistency for the splitting onset. Furthermore, we find $\Delta_K/\Delta<1$ at low $B$ and $\Delta_K/\Delta>1$ at high $B$, where $\Delta$ is the Zeeman energy of the bare spin. We discuss an approximate scaling of $\Delta_K$ with $B/T_K$ at low $B$ and compare the findings to previous measurements and theory.