Frequency Regimes of Kondo Dynamics in a Single-Electron Transistor

It has been theoretically predicted that the Kondo temperature, T$_K$, serves as the intrinsic timescale for the formation of Kondo correlations between conduction electrons and local spin moments. To probe this timescale, we have measured the time averaged differential conductance, $\langle$G$\rangle$=d$\langle$I$\rangle$/dV$_{ds}$, of a single electron transistor in the spin 1/2 Kondo regime in presence of an oscillating bias voltage, V(t)=V$_{ds}$+V$_{AC}$ sin(2$\pi$ft). We present the amplitude dependent conductance over select frequencies spanning several orders of magnitude below T$_K$ to twice T$_K$ (T$_K \sim$ 16GHz). At frequencies above T$_K$, we find good agreement with theory [Kaminski, et al. Phys. Rev. B 62, 8154 (2000)] in both the low (V$_{AC} \sim$ T$_K$/10) and high (V$_{AC} \sim$ 10T$_K$) amplitude regimes. The onset of non-adiabatic conductance behavior occurs well below prediction, f $\sim$ T$_K$, and becomes more apparent as the frequency nears T$_K$.