Sondheimer oscillations as a probe of non-ohmic flow in type-II Weyl semimetal WP\(_2\)

• Published in: arXiv.org 2020-12
• Main Authors: van Delft, Maarten R, Wang, Yaxian, Putzke, Carsten, Oswald, Jacopo, Varnavides, Georgios, Garcia, Christina A C, Guo, Chunyu, Schmid, Heinz, Süss, Vicky, Borrmann, Horst, Diaz, Jonas, Sun, Yan, Felser, Claudia, Gotsmann, Bernd, Narang, Prineha, Moll, Philip J W
• Format: Article
• Language: English
• Subjects: Conductors; Electronic devices; Electrons; High temperature; Magnetoresistance; Magnetoresistivity; Momentum; Nanotechnology devices; Ohm's Law; Oscillations; Parameter identification; Phonons; Scattering; Transport phenomena
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2012.08522

As conductors in electronic applications shrink, microscopic conduction processes lead to strong deviations from Ohm's law. Depending on the length scales of momentum conserving (\(l_{MC}\)) and relaxing (\(l_{MR}\)) electron scattering, and the device size (\(d\)), current flows may shift from ohmic to ballistic to hydrodynamic regimes and more exotic mixtures thereof. So far, an in situ, in-operando methodology to obtain these parameters self-consistently within a micro/nanodevice, and thereby identify its conduction regime, is critically lacking. In this context, we exploit Sondheimer oscillations, semi-classical magnetoresistance oscillations due to helical electronic motion, as a method to obtain \(l_{MR}\) in micro-devices even when \(l_{MR}\gg d\). This gives information on the bulk \(l_{MR}\) complementary to quantum oscillations, which are sensitive to all scattering processes. We extract \(l_{MR}\) from the Sondheimer amplitude in the topological semi-metal WP\(_2\), at elevated temperatures up to \(T\sim 50\)~K, in a range most relevant for hydrodynamic transport phenomena. Our data on micrometer-sized devices are in excellent agreement with experimental reports of the large bulk \(l_{MR}\) and thus confirm that WP\(_2\) can be microfabricated without degradation. Indeed, the measured scattering rates match well with those of theoretically predicted electron-phonon scattering, thus supporting the notion of strong momentum exchange between electrons and phonons in WP\(_2\) at these temperatures. These results conclusively establish Sondheimer oscillations as a quantitative probe of \(l_{MR}\) in micro-devices in studying non-ohmic electron flow.