Opportunities of topological semimetals as novel material for computing. Experimental transport studies and devices

Abstract

Topological materials have attracted strong interest in recent years due to their exotic transport properties set by non-trivial band structures. These materials were shown to exhibit exceptional properties such as high electron mobilities and large magnetoresistance, for example. Among the many identified semimetal compounds, we will focus on our recent work involving the two semimetals NbP and CoSi to highlight promising applications. NbP was selected due to the high magnetoresistance and demonstrated to modulate a current in a transistor configuration with very high efficiency. The chiral semimetal cobalt monosilicide (CoSi) has been identified as a prototype for topological materials exhibiting extremely long Fermi arc surface states. However, CoxSi1-x is stable at various stoichiometries and defect densities, the effect of which on topological and normal magnetotransport is little explored. We show a study of CoSi samples ranging from single crystals, via textured polycrystalline films to amorphous thin films grown using molecular beam epitaxy. Exhaustive structural characterization (STEM, AFM, XRD) and chemical analysis (XPS, SIMS, EDS, RBS) enable a detailed correlation to transport as a function of magnetic field, temperature and dimension. This enables us to relate anomalous Hall effects, quantum anomalies in longitudinal and transverse magnetoresistance, quantum oscillations, as well as unconventional size-scaling of conductivity down to the nm-range to structure and composition. As expected from the band structure, transport in CoSi is remarkable in many aspects.