Transport investigation of topological materials

Materials with non-trivial electronic band topology have garnered significant attention over the past decade due to their unique properties. Compounds such as WTe2, MoTe2, TaIrTe4, and TaRhTe4, characterized by substantial spin-orbit coupling, exhibit topologically non-trivial features, leading to unconventional magneto-transport phenomena. Furthermore, their semimetallic nature with high carrier mobility makes them promising candidates for enhanced magneto-thermoelectric effects. Interestingly, these compounds belong to the family of layered van der Waals materials, which are highly tunable by controlling the number of layers. To fully exploit the advantageous properties of this material family, it is essential to understand their electric and thermoelectric transport characteristics. In this thesis, we systematically investigate the magneto-transport coefficients on telluride-based van der Waals type-II Weyl semimetals as a function of different tuning parameters including temperature, magnetic field, and uniaxial strain. Our sample set includes TaRhTe4, TaIrTe4, TaRh0.3Ir0.7Te4, W0.65Mo0.35Te2, and Ta1.25Ru0.75Te4 compounds. A semiclassical approach was employed to interpret the results. Standard electric transport measurements with out-of-plane magnetic fields show no evidence of anomalous behavior attributable to the topologically non-trivial nature of Weyl semimetals in TaRhTe4, TaIrTe4, TaRh0.3Ir0.7Te4, andW0.65Mo0.35Te2 compounds. However, when the magnetic field was aligned in-plane, parallel to the current density vector (i.e., along the electric field), we observed negative magnetoresistance in the TaRhTe4 and TaRh0.3Ir0.7Te4 compounds. This negative magnetoresistance is attributed to the chiral anomaly, providing evidence of non-trivial topological behavior. Thermoelectric transport measurements revealed no anomalies related to non-trivial topology for TaRhTe4, TaIrTe4, TaRh0.3Ir0.7Te4, andW0.65Mo0.35Te2 compounds. However, while Nernst effect measurements for TaRh0.3Ir0.7Te4 compounds exhibit a standard linear behavior with the magnetic field, a super-linear contribution to the Nernst effect was observed at low temperatures for TaRhTe4, TaIrTe4, and W0.65Mo0.35Te2 compounds, potentially arising from several factors, including strong compensation between electron-like and hole-like carriers, topological Weyl crossings near the Fermi level, or impurity band effects causing multiband behavior. Within our sample set (TaRhTe4, TaIrTe4, W0.65Mo0.35Te2, compared to WTe2 and MoTe2), we established a correlation between the dominant linear-in-magnetic-field Nernst coefficient and mobility, consistent with established Nernst scaling frameworks, albeit with a modified scaling factor compared to existing literature. Our Hall and Nernst measurements for Ta1.25Ru0.75Te4 show clear evidence of anomalous transport contributions stemming from the Berry curvature, suggesting non-trivial topology. Finally, elasto-transport measurements revealed a substantial change of the Nernst coefficient of WTe2 compound due to the application of uniaxial strain, evidencing that elasto-thermoelectric transport can be a sensitive probe to evaluate the susceptibility of the electronic properties of such materials to mechanical deformations.