Advances in ultraclean materials with very long electron mean-free paths, including GaAs/AlGaAs heterostructures and graphene, have opened new opportunities to study electronic transport beyond the conventional Ohmic regime. We experimentally investigate transport in 2D GaAs/AlGaAs electron systems, with mean-free paths 100 micron or longer at cryogenic temperatures, across ballistic, hydrodynamic and diffusive regimes using mesoscopic nonlocal device geometries. While diffusive transport with strong momentum dissipation is governed by local current-field relations, momentum-conserving ballistic and hydrodynamic transport exhibit pronounced nonlocal behavior. In the hydrodynamic regime, electron-electron interactions lead to viscous behavior with unusual properties such as the formation of current vortices and negative nonlocal resistances. Complementary Boltzmann-equation simulations provide detailed maps of current density and electrostatic potential, enabling direct comparison with experiments. Beyond shaping collective flow, electron-electron interactions determine the fundamental quasiparticle lifetime in a Fermi liquid. By exploiting ballistic transport as a precision probe of interaction-driven scattering, we have quantified electron-electron interactions and found results consistent with Fermi liquid behavior. Yet the results also indicate that distinct interaction length scales may govern viscous transport. To change the electron temperature we drive the electron system out of equilibrium, strongly affecting electron-electron interactions. In this regime we demonstrate obligate nonlinearities in the current-voltage relations. While the studies advance the fundamental understanding of nonequilibrium electron dynamics and quasiparticle lifetimes, the results also contribute to the development of low-dissipation cryoelectronic technologies for quantum systems.
Prof. Jean J. Heremans obtained his PhD at Princeton University, in experimental solid-state physics and low-temperature physics. After a postdoctoral stay at the National High Magnetic Field Laboratory and Florida State University in Tallahassee (FL) working on nanoscale magnets and spintronics, he joined a medium-sized semiconductor company in NJ. There for a few years he was involved in optimizing the electronic properties of III-V semiconductors, particularly InSb, for applications in magnetic sensors, which were commercially successful. Subsequently he joined Ohio University’s Department of Physics and Astronomy as faculty member, and was the founding director of the Nanoscale and Quantum Phenomena Institute. In 2005, as associate professor he joined Virginia Tech’s Department of Physics, where he presently is Professor of Physics. At Virginia Tech he leads the Quantum Matter and Nanodevices Lab, where the research centers on quantum electronic phenomena in the solid-state, new electronic transport effects, spintronics, quantum materials, electron quantum coherence, sensors and nanoelectronic devices.