• Control of electron-electron interaction in graphene by proximity screening

      Kim, M.; orcid: 0000-0001-6304-6901; Xu, S. G.; orcid: 0000-0002-0589-5291; Berdyugin, A. I.; Principi, A.; Slizovskiy, S.; Xin, N.; Kumaravadivel, P.; orcid: 0000-0002-9817-1697; Kuang, W.; orcid: 0000-0003-4309-365X; Hamer, M.; Krishna Kumar, R.; et al. (Nature Publishing Group UK, 2020-05-11)
      Abstract: Electron-electron interactions play a critical role in many condensed matter phenomena, and it is tempting to find a way to control them by changing the interactions’ strength. One possible approach is to place a studied system in proximity of a metal, which induces additional screening and hence suppresses electron interactions. Here, using devices with atomically-thin gate dielectrics and atomically-flat metallic gates, we measure the electron-electron scattering length in graphene and report qualitative deviations from the standard behavior. The changes induced by screening become important only at gate dielectric thicknesses 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 electron-electron scattering in graphene superlattices. The results provide a guidance for future attempts to achieve proximity screening of many-body phenomena in two-dimensional systems.
    • Water friction in nanofluidic channels made from two-dimensional crystals

      Keerthi, Ashok; Goutham, Solleti; You, Yi; Iamprasertkun, Pawin; orcid: 0000-0001-8950-3330; Dryfe, Robert A. W.; orcid: 0000-0002-9335-4451; Geim, Andre K.; orcid: 0000-0003-2861-8331; Radha, Boya; orcid: 0000-0003-1345-7029; email: radha.boya@manchester.ac.uk (Nature Publishing Group UK, 2021-05-25)
      Abstract: Membrane-based applications such as osmotic power generation, desalination and molecular separation would benefit from decreasing water friction in nanoscale channels. However, mechanisms that allow fast water flows are not fully understood yet. Here we report angstrom-scale capillaries made from atomically flat crystals and study the effect of confining walls’ material on water friction. A massive difference is observed between channels made from isostructural graphite and hexagonal boron nitride, which is attributed to different electrostatic and chemical interactions at the solid-liquid interface. Using precision microgravimetry and ion streaming measurements, we evaluate the slip length, a measure of water friction, and investigate its possible links with electrical conductivity, wettability, surface charge and polarity of the confining walls. We also show that water friction can be controlled using hybrid capillaries with different slip lengths at opposing walls. The reported advances extend nanofluidics’ toolkit for designing smart membranes and mimicking manifold machinery of biological channels.