Askhat K. Bakarov

A nanomechanical resonator provides a simple way to directly measure the torque generated by electron vortices.

Hydrodynamic electron transport in solids, governed by momentum-conserving electron-electron collisions, offers a unique framework to explore collective phenomena. Within this framework, correlated electron motion is modeled as viscous fluid flow, with viscosity serving as the interaction parameter. Advances in electron hydrodynamics remain constrained by two unresolved issues: the questionable existence of materials with intrinsically smooth boundaries enabling perfect slip in electron fluids and the lack of quantitative experimental confirmation of the theoretical relation linking the viscosity to electron-electron scattering length. Here, we resolve this through measurements of these quantities in the same electron system in GaAs/AlGaAs heterostructure. Our experiments reveal large flow slippage at boundaries of microscale constrictions-an unexpected phenomenon for electron liquid that parallels ultrafast water transport in carbon nanotubes. These findings bridge the fields of electron hydrodynamics and nanofluidics, highlighting the transformative potential of hydrodynamic engineering across condensed matter and fluidic technologies.

Nanoelectromechanical systems based on (Al,Ga)As/GaAs heterostructures with a two-dimensional electron gas can rely on both piezoelectric and electrostatic driving and detection. While this multifunctionality may be beneficial, disentanglement of these two physical mechanisms is important. In a multi-mode nanoelectromechanical system, we experimentally discern the electrostatic and piezoelectric effects in various configurations. A well-controlled system relying entirely on the electrostatic effect is demonstrated, where a field-effect transistor reads out the oscillations of its cantilevered side gate. We show that, apart from the two mentioned mechanisms, an additional time-delayed driving force arises due to the generation of bulk acoustic waves in the entire chip.

We demonstrate the crucial role of small-angle scattering in transverse magnetic focusing (TMF) in ballistic GaAs/AlGaAs heterostructures. Measurements in various samples show that the role significantly depends on their geometry. We propose a phenomenological model parameterizing this dependence with the angular acceptance of the detecting contact. This model is consistent with the diversity of experimental data and, therefore, enables accurate extraction of the key characteristic of inter-electron (e–e) interaction—the e–e scattering length—from TMF experiment, thus turning it into a uniquely effective tool for studying e–e scattering.