Spring 2025 Bethe Lecture Series- LASSP Special Seminar:

Professor Shahal Ilani, Department of Condensed Matter Physics, Weizmann Institute of Science

Title: What Is the Ultimate Conductance of Hydrodynamic Electrons?

Abstract:

Electrical resistance usually originates from lattice imperfections. However, even a perfect lattice has a fundamental resistance limit, given by the Landauer conductance of its discrete modes. This resistance, shown by Sharvin to appear at the contacts to electronice devices , sets the ultimate conduction limit of non-interacting electrons. Recent years have seen growing evidence of hydrodynamic electronic phenomena, prompting recent theories ot ask whether liquid electrons can radically break this fundamental Landauer-Sharvin limit. In this talk, I will present imaging experiments of electronic flows in high-mobility graphene Corbino devices to answer this question. First, by imaging ballistic flows at low temperatures, we observe a Landauer-Sharvin resistance that does not appear at contacts but is instead distributed throughout the bulk. This underpins the phase-space origin of this resistance-as emerging from spatial gradients in the number of conduciton modes. At elevated temperatures, we identify and account for the contribution of electron-phonon scattering and reveal the pure hydrodynamic flow. Strikingly, we find that hydrodynamic electron flow eliminates completely the bulk Landauer-Sharvin resistance. Finally, by adding small magnetic fields , we image swirling magneto-hydrodynamic flows, revealing the key emergent length-scale predicted by hydrodynamic theories-the Gurzhi length. These observations demonstrate that electronic fluids can dramatically overcome the limiations of ballistic electrons, with important implications for fundamental science and future technologies.

Hosted By: Katja Nowack