Strong interlayer charge transfer due to exciton condensation in an electrically isolated GaAs quantum well bilayer

Abstract

We introduce a design of electrically isolated "floating" bilayer GaAs quantum wells (QW) in which application of a large gating voltage controllably and highly reproducibly induces charges that remain trapped in the bilayer after removal of the gating voltage. At smaller gate voltages, the bilayer is fully electrically isolated from external electrodes by thick insulating barriers. This design permits full control of the total and differential densities of two coupled 2D electron systems. The floating bilayer design provides a unique approach for studying systems inaccessible by simple transport measurements. It also provides the ability to measure the charge transfer between the layers, even when the in-plane resistivities of the 2D systems diverge. We measure the capacitance and inter-layer tunneling spectra of the QW bilayer with independent control of the top and bottom layer electron densities. Our measurements display strongly enhanced inter-layer tunneling current at 𝑣 = 1, a signature of exciton condensation of a strongly interlayer-correlated bilayer system. With fully tunable densities of individual layers, the floating bilayer QW system provides a versatile platform to access previously unavailable information on the quantum phases in electron bilayer systems.Weakly coupled quantum Hall (QH) bilayer systems display a variety of exotic phases as the filling factor of the two layers vary [1][2][3]. Under quantizing magnetic fields, decreasing the separation distance of two layers to become comparable to the mean interparticle spacing can drive the double layer system into phases not possible in single layers [4][5][6]. When the individual layers are in strongly intra-layer correlated states such as fractional quantum Hall phases, the additional interlayer coupling can play a non-trivial role that modifies the properties of the phases or

Quantum-metric-enabled exciton condensate in double twisted bilayer graphene

“…The results present a comprehensive and detailed picture of the possible correlated states of double-twisted bilayer graphene and show the role played by the quantum metric on the stability and T BKT of the exciton condensate in double-twisted bilayer graphene and so should constitute a useful guide to experimentalists studying the correlated phases of these novel systems. In a more general context, our findings point to the importance of the quantum metric for the understanding of the physics of ECs in flat-band systems, including QH and moiré bilayers [58][59][60].…”