Physical Society Colloquium

Superconductivity versus the Quantum Hall Effect

Jim Eisenstein

Caltech

A two-dimensional electron gas exhibiting the quantum Hall effect is a topological insulator: Current cannot pass through its interior even though perfectly conducting one-dimensional states swirl around at its boundary.

In this talk I will describe a long-running series of experiments on an unusual quantum Hall state which occurs in double layer two-dimensional electron systems. Although it too is a topological insulator, it differs from all other quantum Hall systems in that it possesses a spontaneously phase coherent condensate. This condensate closely resembles the Cooper pair condensate in a superconductor, except that the paired objects are charge neutral electron-hole pairs, i.e. excitons.

While a condensate of neutral excitons may sound pretty useless, our most recent experiments have convincingly shown that they can flow unimpeded through the insulating bulk of the quantum Hall liquid and deliver energy to remote locations. Indeed, a remarkable analogy exists between these results and a battery delivering energy to a remote resistive load via two superconducting wires.