Universal Negative Correlation between Nonreciprocity and Superconducting Transition Width in FeTe-Based Heterostructures

Abstract

Nonreciprocal charge transport in noncentrosymmetric superconductors probes broken symmetries and superconducting fluctuations and underpins the superconducting diode effect. Despite extensive studies, the factors governing its magnitude remain unclear. In this work, we use molecular beam epitaxy (MBE) to synthesize a broad family of FeTe-based superconducting heterostructures with top layers spanning topologically trivial versus nontrivial, layered versus nonlayered, and magnetic versus nonmagnetic materials. Through systematic first- and second-harmonic transport measurements, we find that the magnetochiral anisotropy coefficient $γ$ is insensitive to the top-layer crystal structure, lattice constant, thickness, topology, and magnetism, but exhibits a negative correlation with the superconducting transition width $ΔT$. Control measurements on superconducting stoichiometric FeTe films reveal much weaker nonreciprocity, confirming the essential role of interfacial inversion-symmetry breaking. Combined with a disorder-based theoretical model, our results establish a universal relationship: for comparable inversion-symmetry breaking, reduced interfacial disorder sharpens the superconducting transition and strongly enhances nonreciprocal transport in the Berezinskii-Kosterlitz-Thouless (BKT) transition regime. These findings identify $ΔT$ as a unifying parameter governing nonreciprocity across FeTe-based heterostructures, reconcile previously disparate observations, and establish a general framework for engineering enhanced nonreciprocal superconducting responses and exploring superconducting diode effects in nonlinear quantum devices.