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تسجيل مستخدم جديدPossible Topological Phase Transition in Fe-Vacancy-Ordered $beta$-Fe$_{4+delta}$Se$_{5}$ Nanowires
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We studied the electrical transport on $beta$-Fe$_{4+delta}$Se$_{5}$ single-crystal nanowires, exhibiting $sqrt{5}timessqrt{5}$ Fe-vacancy order and mixed valence of Fe. We observed a first-order metal-insulator transition of the transition temperature at $sim$28~K at zero magnetic field. The dielectric relaxation reveals that the transition is related to an energy gap expansion of $sim$12~meV, involving the charge-orbital ordering. At nearly 28~K, colossal positive magnetoresistance emerges, resulting from the magnetic-field dependent shift of the transition temperature. Through the transition, the magnetotransport behavior transits from two-dimension-like to one-dimension-like conduction. The transition temperature demonstrates anisotropy with the $c$-axis as the preferred orientation in magnetic fields, suggesting the spin-orbital coupling. Our findings demonstrate the novel magnetoresistive transition intimating a topological transition in the Fe-vacancy-ordered $beta$-Fe$_{4+delta}$Se$_{5}$ nanowires. The results provide valuable information to better understand the orbital nature and the emergence of superconductivity in FeSe-based materials.
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