Resistive signature of excitonic coupling in an electron-hole double layer with a middle barrier

We study the interlayer scattering mediated by long-range Coulomb interaction between electrons (density $n)$ and holes $(p)$ in a double-layer system. The gated device is made of InAs $(e)$ and InGaSb $(h)$ quantum wells separated by a AlSb middle barrier such that the interlayer tunneling is negligibly small. By using independent-layer contacts we measure the transport tensors $\phantom{\rule{4pt}{0ex}}{\ensuremath{\rho}}_xx$ and ${\ensuremath{\rho}}_xy$ that are solely from the InAs layer, while sweeping $p$ in the InGaSb layer. We find a strongly enhanced resistive scattering signal as the carrier densities approach a total charge neutrality, $n=p$, which cannot be described by the Fermi-liquid theory. Results of data analysis for density, temperature, and magnetic field dependences are consistent with the emergence of excitonic coupling between the two layers, stressing the dominance of Coulomb interaction even in the presence of disorder.