Intertwined Topological Phases in TaAs₂ Nanowires with Giant Magnetoresistance and Quantum Coherent Surface Transport

Nanowires (NWs) of topological materials are emerging as an exciting platform to probe and engineer new quantum phenomena that are hard to access in bulk phase. Their quasi-1D geometry and large surface-to-bulk ratio unlock new expressions of topology and highlight surface states. TaAs₂, a compensated semimetal, is a topologically rich material harboring nodal-line, weak topological insulator (WTI), C₂-protected topological crystalline insulator, and Zeeman field-induced Weyl semimetal phases. We report the synthesis of TaAs₂ NWs in situ encapsulated in a dielectric SiO₂ shell, which enable to probe rich magnetotransport phenomena, including metal-to-insulator transition and strong signatures of topologically nontrivial transport at remarkably high temperatures, direction-dependent giant positive, and negative magnetoresistance, and a double pattern of Aharonov-Bohm oscillations, demonstrating coherent surface transport consistent with the two Dirac cones of a WTI surface. The SiO₂-encapsulated TaAs₂ NWs show room-temperature conductivity up to 15 times higher than bulk TaAs₂. The coexistence and susceptibility of topological phases to external stimuli have potential applications in spintronics and nanoscale quantum technology.