Quantum Hall effect of the topological insulator state of cadmium arsenide in Corbino geometry

The surfaces of a three-dimensional topological insulator each host single Dirac fermion, which, in strong magnetic field, contribute to the transverse conductance integer-and-a-half multiples quantum. direct observation this extra half integer, hallmark two-dimensional state, is usually thwarted by fermion doubling theorem—top and bottom are not measured independently. Here, we employ Corbino measurement geometry which current, induced an ac driven around ring, as complementary conventional Hall bar geometry. As device enters quantum regime, voltage reaches series plateaus when current carried incompressible bulk states. We compare results with corresponding measurements.