European Research Council Starter Grant 2016 goes to mqm!

We are happy and excited about the decision of the ERC to fund a new project on microstructured topological matter (“MiTopMat”). In this five year project, we will investigate the transport properties of novel topological states such as the Fermi arc surface states. By designing microstructures on the length scale at or below the mean free path of electrons we look for new electronic behavior to understand their properties and search for potential applications in future electronics.

Thanks to the team for all your hard work!

Hydrodynamic currents in PdCoO2 published in Science

We have investigated how electric currents flow through FIB-fabricated microconstrictions in ultra-pure crystals of the delafossite PdCoO2. As the channel width becomes narrower and narrower, the sample enters the ballistic regime when it becomes thinner than the bulk mean free path (which is at 20 micron insanely high in this material). In ballistic transport, the dominant source of scattering is boundary scattering, and simple phase space calculations give a clear theoretical prediction how the resistance should scale with channel width in this case, which has been observed in many materials.

Our experiments show clear deviations from this classical scaling, that clearly contradict the expectations for ballistic current flow. The results can be quantitatively explained though if one assumes a viscous contribution to the electron flow arising from electron-electron interactions. It turns out that the electronic liquid in PdCoO2 at 2K has a similar viscosity to that of water at room temperature!

First magnet system goes online!

Our first 8T superconducing magnet goes online and was tested to peak field without any issues. This wide-bore magnet will feature a special vibration-isolated cryostat, enabling challenging transport, elastic modulus and heat capacity measurements in a temperature range between 1.5K-300K. Built from various salvaged parts of old magnet systems, it was named after the king of Saxony “Johann der Beständige” (1525 – 1532). To many more years of operation of “John the enduring”!

Hydrodynamic signatures in electron flow

We investigate to what extent electrons in very clean metals with high electron-electron scattering rates can exhibit well-known phenomena from hydrodynamics. Here we made a “stacked-funnel” structure from PdCoO2, searching for the appearance of vortices and turbulence as the electronic “liquid” flows through the structure.