Impact of Heterostructure Design on Transport Properties in the Second Landau Level of In Situ Back-Gated Two-Dimensional Electron Gases

We report on transport in the second Landau level in in situ back-gated two-dimensional electron gases in GaAs/AlxGa1-xAs quantum wells. Minimization of gate leakage is the primary heterostructure design consideration. Leakage currents resulting in dissipation as small as similar to 10 pW can cause noticeable heating of the electrons at 10 mK, limiting the formation of novel correlated states. We show that when the heterostructure design is properly optimized, gate voltages as large as 4 V can be applied with negligible gate leakage, allowing the density to be tuned over a large range from depletion to over 4 x 10(11) cm(-2). As a result, the strength of the nu = 5/2 state can be continuously tuned from onset at n similar to 1.2 x 10(11) cm(-2) to a maximum Delta(5/2) = 625 mK at n = 3.35 x 10(11) cm(-2). An unusual evolution of the reentrant-integer quantum Hall states as a function of density is also reported. These devices can be expected to be useful in experiments aimed at proving the existence of non-Abelian phases useful for topological quantum computation.