Kondo-Temperature Dependence of the Magnetic-Field Splitting of a Kondo Peak in a Single-Electron Transistor

We present a detailed study of the Kondo peak splitting as a function of Kondo temperature $T_{K}$ and magnetic field $B$ parallel to the 2DEG in an AlGaAs/GaAs single-electron transistor. We observe that, at fixed $B$, the Kondo splitting decreases logarithmically with Kondo temperature, in agreement with theory. However, we find that the magnitude of the prefactor of the logarithm is much larger than predicted. We also find that there exists a critical magnetic field $B_{c}$ below which the Kondo peak does not split, in qualitative agreement with theory. However, our results indicate that $B_{c}$ is smaller than predicted. These measurements show that the theory of non-equilibrium Kondo physics is still incomplete.