Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies of collective behavior driven by inter-layer Coulomb coupling. Here we report heterostructures comprising a single-layer (or bilayer) graphene carrying a fluid of massless (massive) chiral carriers, and a quantum well created in GaAs 31.5 nm below the surface, supporting a high-mobility two-dimensional electron gas. These are a new class of double-layer devices composed of spatially-separated electron and hole fluids. We find that the Coulomb drag resistivity significantly increases for temperatures below 5-10 K, following a logarithmic law. This anomalous behavior is a signature of the onset of strong inter-layer correlations, compatible with the formation of a condensate of permanent excitons. The ability to induce strongly-correlated electron-hole states paves the way for the realization of coherent circuits with minimal dissipation and nanodevices including analog-to-digital converters and topologically protected quantum bits.
@article{arxiv.1401.0902,
title = {Electron-hole pairing in graphene-GaAs heterostructures},
author = {A. Gamucci and D. Spirito and M. Carrega and B. Karmakar and A. Lombardo and M. Bruna and A. C. Ferrari and L. N. Pfeiffer and K. W. West and Marco Polini and V. Pellegrini},
journal= {arXiv preprint arXiv:1401.0902},
year = {2015}
}