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arXiv · 2610.27729

Superconducting weak links at substrate steps in bilayer nickelate films

Yidi Liu·Yaoju Tarn·Lopa Bhatt·Puhua Zhang·Joonseo Song·Berit H. Goodge·David A. Muller·Harold Y. Hwang·Yijun Yu
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Abstract

Ambient-pressure superconductivity above 40 K has been realized in bilayer nickelate thin films on SrLaAlO$_4$ (001), yet resistive measurements often exhibit incomplete zero-resistance states and/or two-step superconducting transitions of unresolved origin. We show that these features arise from superconducting weak links at substrate step-terrace structures. A direct correlation between the azimuthal-angle-dependent two-step transition and step-terrace orientation establishes this connection, further supported by atomic-scale visualization of structurally disrupted regions at step terraces. Modeling the films as pristine (weak-link) regions with higher (lower) transition temperature reproduces essential features of the two-step transition using both a simple model and finite-element simulations. Transport measurements further reveal a strong dependence of transition characteristics - and even the occurrence of superconductivity itself - on average terrace width. These results identify step-induced weak links as the microscopic origin of two-step transitions in bilayer nickelate films, providing a framework for understanding anisotropic and percolative transport, and a route to superconducting devices.

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Yidi Liu, Yaoju Tarn, Lopa Bhatt, Puhua Zhang, Joonseo Song, Berit H. Goodge, David A. Muller, Harold Y. Hwang, Yijun Yu. 2026-10-20. Superconducting weak links at substrate steps in bilayer nickelate films. https://doi.org/10.1021/acs.nanolett.6c03024

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