Coherent subgap transport in spin-split Josephson junctions

David Caldevilla-Asenjo; Gorm Ole Steffensen; Sara Catalano; Alberto Hijano; Maxim Ilyn; Celia Rogero; Ramon Aguado; F. Sebastian Bergeret; Alfredo Levy Yeyati

arXiv · 2511.23359

Coherent subgap transport in spin-split Josephson junctions

David Caldevilla-Asenjo·Gorm Ole Steffensen·Sara Catalano·Alberto Hijano·Maxim Ilyn·Celia Rogero·Ramon Aguado·F. Sebastian Bergeret·Alfredo Levy Yeyati

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Abstract

We report the first experimental observation of subgap transport in ferromagnetic insulator/superconductor/insulator/superconductor junctions realized in EuS/Al/AlOx/Al vertical stacks. Differential conductance measurements reveal multiple Andreev reflection peaks, with odd-order peaks split by the spin-splitting induced in the superconductor adjacent to EuS, while even-order peaks remain unaffected. Combining experiments with quasiclassical transport modeling, we extract the spin-splitting and the distribution of transmission channels, finding that a significant fraction ($\sim 23\%$) of highly transparent channels ($\tau \approx 0.9$) dominates transport. The observation of a Josephson current further confirms strong superconducting coupling through these channels. Our results demonstrate that a single spin-split superconductor is sufficient to observe the even-odd MAR effect. Our work establishes EuS/Al junctions as a versatile platform to study subgap transport, Josephson coupling, and spin-polarized superconducting phenomena.

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David Caldevilla-Asenjo, Gorm Ole Steffensen, Sara Catalano, Alberto Hijano, Maxim Ilyn, Celia Rogero, Ramon Aguado, F. Sebastian Bergeret, Alfredo Levy Yeyati. 2025-11-28. Coherent subgap transport in spin-split Josephson junctions. https://arxiv.org/abs/2511.23359

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