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Description
Altermagnets (AMs) [1] have recently emerged as a promising platform in condensed matter physics, with possible applications in multilayer nanostructures such as magnetic superconducting tunnel junctions [2]. Compared with ferromagnets (Fs), which are commonly employed in a similar fashion [3], altermagnets offer the key advantage of vanishing macroscopic magnetization—a property that enhances their compatibility with superconductivity, while still enabling spin-polarized transport.
In this work, we theoretically investigate the transport properties of a three-dimensional vertical tunnel junction comprising semi-infinite AM and s-wave superconductor (S) electrodes; the interface between the two electrodes is modeled as a thin tunneling barrier that induces Rashba spin-orbit coupling (SOC). By computing the conductance spectra of the AM/S junction for realistic parameter regimes and for different orientations of the spin-split altermagnetic Fermi surfaces relative to the interface, we identify experimentally accessible signatures to map the conductance features to the underlying Fermi-surface structure of the AM.
Furthermore, we analyze unconventional Andreev reflections at the interface, which can generate a spin-polarized triplet supercurrent in the intrinsically singlet s-wave S mediated by SOC-induced spin flips. We examine the angular dependence of these unconventional Andreev reflections—and consequently, the efficiency of triplet-pair generation—upon rotating the spin-split Fermi surfaces with respect to the interface. Our results are finally contrasted with the well-established behavior of ferromagnetic F/S junctions [3].
This project is supported by the Slovak Research and Development Agency under Contract No. APVV-23-0515, and Deutsche Forschungsgemeinschaft (DFG; German Research Foundation)—Grants 454646522; 314695032.
[1] L. Šmejkal, J. Sinova, T. Jungwirth, Emerging Research Landscape of Altermagnetism, Phys. Rev. X 12, 040501 (2022).
[2] M. Papaj, Andreev reflection at the altermagnet-superconductor interface, Phys. Rev. B 108, L060508 (2023), and the references therein.
[3] P. Högl, A. Matos-Abiague, I. Žutić, J. Fabian, Magnetoanisotropic Andreev Reflection in Ferromagnet-Superconductor Junctions, Phys. Rev. Lett. 115, 116601 (2015).