Origin of Nonreciprocal Transport in Superconducting FeTe Heterostructures

Nonreciprocal charge transport has been studied in various superconducting systems, yet its microscopic origin remains debated. In this work, we employ molecular beam epitaxy (MBE) to synthesize a series of FeTe heterostructures by stacking different top-layer materials on a FeTe layer. We investigate non-topological layers, including Pb_1-xSn_xTe (x < 0.4) and CrTe₂, as well as topological insulator Bi₂Te₃ and topological crystalline insulators Pb_1-xSn_xTe (x ≥ 0.4). By performing electrical transport measurements, we find that all FeTe heterostructures: Pb_1-xSn_xTe/FeTe, CrTe₂/FeTe, and Bi₂Te₃/FeTe, reach a zero resistance state. Second harmonic measurements on these heterostructures reveal that a large magnetochiral anisotropy coefficient γ (~20-70×10^-3 T ^-1A ^-1m) occurs in samples with sharper superconducting transitions. These results indicate that topological surface states are not required to achieve strong nonreciprocal transport. Instead, the enhanced γ appears independent of the top-layer material and is likely determined by the robustness of emergent superconductivity in FeTe heterostructures.