1304.0037 (Bryan Hemingway et al.)

Non-Monotonic Dynamic Conductance in the Spin-1/2 Kondo Regime in a
Single-Electron Transistor    [PDF]

Bryan Hemingway, Stephen Herbert, Michael Melloch, Andrei Kogan

We present measurements of time-averaged differential conductance $G$ in a single-electron transistor tuned to the spin 1/2 Kondo regime and demonstrate an anomalous non-monotonic dependence of $G$ on frequency, indicating a change in the density of states in the dynamic regime. At zero external magnetic field, we vary the frequency and amplitude of bias oscillations and identify a suppression of $G$ when the photon energy $hf$ becomes comparable to the Kondo temperature $k_B T_K$. As the frequency increases above $k_B T_K/h$, as well as for bias oscillation amplitudes larger than $k_B T_K/e$ where $e$ is the electron charge, we find that the $G$ approaches the values expected for adiabatic behavior and show that these observations agree with available theoretical predictions. We also report very sharp peaks in the conductance as function of magnetic field which appear at frequencies $f \ge k_B T_K/h$ and are absent at low frequencies. These features are currently not understood.

View original: http://arxiv.org/abs/1304.0037