Tunnelling between the edges of two lateral quantum Hall systems

The edge of a two-dimensional electron system in a magnetic field consists of one-dimensional channels that arise from the confining electric field at the edge of the system(1-3). The crossed electric and magnetic fields caus e electrons to drift parallel to the sample boundary, creating a chiral cur rent that travels along the edge in only one direction. In an ideal two-dim ensional electron system in the quantum Hall regime, all the current flows along the edge(4-6). Quantization of the Hall resistance arises from occupa tion of N one-dimensional edge channels, each contributing a conductance of e(2)/h (refs 7-11), Here we report differential conductance measurements, in the integer quantum Hall regime, of tunnelling between the edges of a pa ir of two-dimensional electron systems that are separated by an atomically precise, high-quality, tunnel barrier. The resultant interaction between th e edge states leads to the formation of new energy gaps and an intriguing d ispersion relation for electrons travelling along the barrier: for example, we see a persistent conductance peak at zero bias voltage and an absence o f tunnelling features due to electron spin, These features are unexpected a nd are not consistent with a model of weakly interacting edge states, Remna nt disorder along the barrier and charge screening may each play a role, al though detailed numerical studies will be required to elucidate these effec ts.