Orbital-driven topological phase transition and planar Hall response in ternary telluride Weyl semimetals

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We study electronic properties of the ternary tellurides TaXTe₄ (X=Rh, Ir) using density functional theory and investigate chiral anomaly mediated planar Hall response from ab initio calculations. We show that TaRhTe₄ is a hybrid Weyl semimetal (WSM), hosting Weyl points (WPs) of both type-I, type-II, and TaIrTe₄ is a type-I WSM in absence of spin-orbit coupling (SOC). TaRhTe₄ continues to remain a hybrid WSM while TaIrTe₄ converts into a type-II WSM under the application of SOC. We observe long Fermi arcs connecting WPs of opposite chirality. We report orbital-driven topological phase transition in ternary tellurides. The WSM phases in TaXTe₄ are controlled by the orbital character of the dxz and dz² states of X=Ir/Rh atoms. Replacing Rh with Ir enhances the dz² orbital contribution near the Fermi level at the expense of dxz states. This transforms the type-I WPs into type-II resulting in a conversion of hybrid WSM TaRhTe₄ to type-II WSM TaIrTe₄. This systematic study opens new routes for engineering topological materials relying beyond strong SOC and sheds light on the effect of orbital degree of freedom on the electronic properties of tellurides. We further report an enhancement of planar Hall effects due to orbital-driven topological phase transition in TaXTe₄ and we make resort to a tight-binding model to correlate the above findings with the velocity modulated off-diagonal effective mass anisotropy in different types of WSMs.