We observe the fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor ν=1/2 in two-dimensional hole systems confined to GaAs quantum wells of width 30 to 50 nm and having bilayerlike charge distributions. The ν=1/2 FQHE is stable when the charge distribution is symmetric and only in a range of intermediate densities, qualitatively similar to what is seen in two-dimensional electron systems confined to approximately twice wider GaAs quantum wells. Despite the complexity of the hole Landau level structure, originating from the coexistence and mixing of the heavy- and light-hole states, we find the hole ν=1/2 FQHE to be consistent with a two-component, Halperin-Laughlin (Ψ331) state.

The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D) charged particles at high magnetic fields, is one of the most fascinating, macroscopic manifestations of a many-body state stabilized by the strong Coulomb interaction. It occurs when the filling factor (ν) of the quantized Landau levels (LLs) is a fraction which, with very few exceptions, has an odd denominator. In 2D systems with additional degrees of freedom it is possible to cause a crossing of the LLs at the Fermi level. At and near these crossings, the FQHE states are often weakened or destroyed. Here we report the observation of an unusual crossing of the two lowest-energy LLs in high-mobility GaAs 2D hole systems which brings to life a new even-denominator FQHE at ν = 1/2. arXiv:1401.7742v1 [cond-mat.mes-hall]

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We report on the design and measurement of a superconducting solenoid integrated on chip with a Josephson junction fabricated in a multilayer 250 nm niobium process. The solenoid generates a current-tunable magnetic field parallel to the junction that allows us to fully suppress the dc Josephson current. The magnitude of the generated field is well approximated by a magnetostatic model, and the modulation of the critical current by the generated field agrees well with simulations for our specific junction geometry. This test circuit allows for the characterization of Josephson junctions in an applied magnetic field without requiring an externally supplied field.