Control of electron-electron interaction in graphene by proximity screening

Electron-electron (e-e) interactions play a critical role in many condensed matter phenomena, and it is tempting to gain control of them by changing the interactions’ strength. One possible approach is to place a studied electronic system in a proximity to a metal, which induces additional screening and hence suppresses electron interactions. So far, however, it was not possible to study experimentally the impact of the screening exerted by metallic or dielectric media on the e-e interaction in a crystal. Driving the electron system in graphene in the hydrodynamic regime, we can quantitatively access e-e scattering length l_ee and investigate how screening exerted by such metal gate changes viscous electron flow. Proximity screening is found to enhance l_ee and qualitatively changes its dependence on carrier density. Counterintuitively, the screening becomes important only at gate dielectrics’ thickness of a few nm, much smaller than a typical separation between electrons. Our theoretical analysis agrees well with the scattering rates extracted from measurements of electron viscosity in monolayer graphene and of umklapp e-e scattering in graphene superlattices. The results provide a guidance for future attempts to achieve screening of many-body phenomena in two-dimensional systems.