Second Landau level fractional quantum Hall effects in the Corbino geometry

• Fabrication of the highest-mobility 2DEG Corbino sample ever.
• Observation of 7/2, 5/2, 7/3 and many other FQH states in the Corbino geometry.
• Determination of the energy gap and Arrhenius prefactor in the second Landau Level.
• Important technical proof-of-concept for bulk thermodynamic measurements in the FQH regime.

For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and measurement of a Corbino-geometry sample in an ultra-high mobility GaAs heterostructure, with a focus on transport in the second and higher Landau levels. In particular, we report activation energy gaps of fractional quantum Hall states, with all edge effects ruled out, and extrapolate σ0 from the Arrhenius fits. Our results show that activated transport in the second Landau level remains poorly understood. The development of this Corbino device opens the possibility to study the bulk of the 5/2 state using techniques not possible in other geometries.