Sondheimer oscillations as a probe of non-ohmic electron flow in type-II Weyl semimetal WP2

Abstract

Hydrodynamic flow of electrons has recently been the focus of numerous studies, indicating electrons in condensed matter can exhibit fluid phenomena. Depending on the length scales of momentum conserving (lmc) and relaxing (lmr) scattering and the conductor size (d), current flow may shift from ohmic to ballistic or hydrodynamic. Distinguishing these regimes, however, requires an accurate experimental method to estimate the mean-free-paths. We present Sondheimer oscillations (SO), as a method to obtain lmr even when lmr»d. SO manifest as periodic-in-B oscillations of the resistivity due to helical motion of carriers along a magnetic field. The field sets the cyclotron radius and thus determines at which point the helical motion is cut off by scattering from the device surface, making a positive or negative contribution to the conduction. As this effect requires there to be no scattering in the bulk, it is sensitive to the mean-free-path and enables its extraction. Using WP2 as a model system, we demonstrate the presence of SO and extract lmr over a wide range of temperatures. We find excellent agreement with theoretical predictions, demonstrating the effectiveness of SO as a tool to determine lmr and study non-Ohmic electron flow. *MRvD acknowledges funding from an NWO Rubicon grant