Sideways Tunnelling and Fractional Josephson Frequency in Double Layered Quantum Hall Systems

The $(kkk)$ double layered quantum Hall state has been shown to exhibit many superfluid properties including the appearance of an alternating tunnelling current in response to an external voltage V. Here we propose the notion of "sideways tunnelling", in which a current tunnels between two such $(kkk)$ states through an incompressible fractional quantum Hall state $(mm0)$. We predict the tunnelling current will alternate with a frequency $\om={eV{\o}\hbar m}$, as a consequence of the tunnelling of $e/m$ fractional charges. We also discuss singularities in the tunnelling current noise spectrum and the non-linear I-V curve.