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Register a new userNegative local resistance caused by viscous electron backflow in graphene
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Graphene hosts a unique electron system in which electron-phonon scattering is extremely weak but electron-electron collisions are sufficiently frequent to provide local equilibrium above liquid nitrogen temperature. Under these conditions, electrons can behave as a viscous liquid and exhibit hydrodynamic phenomena similar to classical liquids. Here we report strong evidence for this transport regime. We find that doped graphene exhibits an anomalous (negative) voltage drop near current injection contacts, which is attributed to the formation of submicrometer-size whirlpools in the electron flow. The viscosity of graphenes electron liquid is found to be ~0.1 m$^2$ /s, an order of magnitude larger than that of honey, in agreement with many-body theory. Our work shows a possibility to study electron hydrodynamics using high quality graphene.
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Recent advances in materials science have made it possible to achieve conditions under which electrons in metals start behaving as highly viscous fluids, thicker than honey, and exhibit fascinating hydrodynamic effects. In this short review we provide a popular introduction to the emerging field of electron hydrodynamics.
We report non-local electrical measurements in a mesoscopic size two-dimensional (2D) electron gas in a GaAs quantum well in a hydrodynamic regime. Viscous electric flow is expected to be dominant when electron-electron collisions occur more often than the impurity or phonon scattering events. We observe a negative nonlocal resistance and attribute it to the formation of whirlpools in the electron flow. We use the different nonlocal transport geometries and compare the results with a theory demonstrating the significance of hydrodynamics in mesoscopic samples.
A negative differential resistance (NDR) in a one-dimensional band insulator attached to electrodes is investigated. We systematically examine the effects of an electrode bandwidth and a potential distribution inside the insulator on current-voltage characteristics. We show that, in uncorrelated systems, the NDR is generally caused by a linear potential gradient as well as by a finite electrode bandwidth. In particular, the former reduces the effective bandwidth of the insulator for elastic tunneling by tilting its energy band, so that it brings about the NDR even in the limit of large electrode bandwidth.
We investigate the hydrodynamic flow of strongly interacting Dirac electrons in a nozzle geometry, which can for instance be realized with graphene. We show that a nozzle can induce a transition from subsonic to supersonic flow. This transition causes a shock wave of the electrons downstream of the throat of the nozzle, which is a distinct signature of hydrodynamic transport. We demonstrate that this effect is visible in the voltage profile along the nozzle when applying a bias and thus represents a suitable experimental probe of the hydrodynamic regime. In particular, there is a section of the nozzle with pronounced negative local resistance and a discontinuity of the local voltage induced by the shock wave.
We investigated experimentally the high-temperature electrical resistance of graphene interconnects. The test structures were fabricated using the focused ion beam from the single and bi-layer graphene produced by mechanical exfoliation. It was found that as temperature increases from 300 to 500K the resistance of the single- and bi-layer graphene interconnects drops down by 30% and 70%, respectively. The quenching and temperature dependence of the resistance were explained by the thermal generation of the electron-hole pairs and acoustic phonon scattering. The obtained results are important for the proposed applications of graphene as interconnects in integrated circuits.
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