Robust Spin Splitting and Fermiology in the Layered Altermagnet CoNb4Se8

ABSTRACT Altermagnetism defies conventional classifications of collinear magnetic phases, combining compensated magnetization with momentum‐dependent, nonrelativistic spin splitting. While altermagnetic band splitting has been established in three‐dimensional compounds such as MnTe and CrSb, layered altermagnets remain far less explored spectroscopically. Here, combining termination‐resolved micro‐ARPES, fine photon‐energy mapping, spin‐ARPES, and density functional theory, we map the three‐dimensional fermiology of the layered g ‐wave altermagnet , obtained by ordered Co intercalation of 2H‐. We resolve the spin–split branches of the altermagnetic pairs directly in the raw photoemission spectra and, with spin‐ARPES at these experimentally identified momenta, show the reversal of the spin polarization at opposite momenta and between two regions of the sample, consistent with opposite time‐reversal domains, and its absence along the symmetry‐protected nodal –K direction. We further report a weak low‐temperature anomaly near T 0 ≈ 50–60 K, detected by magnetometry, temperature‐dependent micro‐ARPES, and ultrafast reflectivity, whose microscopic origin remains open. These results provide a momentum‐resolved benchmark of the electronic structure of a layered altermagnet.

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Publication Details

Journal
Advanced Materials
Published
2026-10-18
DOI
https://doi.org/10.1002/adma.75367
Primary Topic
Magnetic properties of thin films
Type
article
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article

Robust Spin Splitting and Fermiology in the Layered Altermagnet CoNb4Se8

Oliver J. Clark, Matteo Calandra, Matthieu Jamet, Andreas Kreisel et al.
Advanced Materials
Magnetic properties of thin films
article

Robust Spin Splitting and Fermiology in the Layered Altermagnet CoNb4Se8

Oliver J. Clark, Matteo Calandra, Matthieu Jamet, Andreas Kreisel, A. Sambri, Siyu Cheng, F. Miletto Granozio, Andrea Locatelli, Lorenzo Del Re, Federico Massimo Mazzolani, Mario Cuoco, Giorgio Sangiovanni, Tevfik Onur Menteş, Chiara Bigi, Tommaso Antonelli, Marta Zonno, Jun Fujii, Davide Romanin, Alessandro De Vita, F. Bertran, Manuel Tuniz, Won Seop Song, Brian M. Andersen, Ilija Zeljkovic, Matthew D. Watson, Ralph Ernstorfer, Mark T. Edmonds, Y. T. Hwang, Luciano Jacopo D’Onofrio, Vincent Polewczyk, I. Vobornik, Alexander LaFleur, P. Orgiani, Federico Motti, Pietro Maria Forcella, Giovanni Vinai, Federico Cilento, Emiliano Di Gennaro, Jill A. Miwa, H. Jacobsen, M. Szpytma, Christopher Candelora, Jun Sung Kim, Muxian Xu, Iulia Cojocariu, Jean‐François Jacquot, J. Jacobsen, My Bang Petersen
article en

Abstract

ABSTRACT Altermagnetism defies conventional classifications of collinear magnetic phases, combining compensated magnetization with momentum‐dependent, nonrelativistic spin splitting. While altermagnetic band splitting has been established in three‐dimensional compounds such as MnTe and CrSb, layered altermagnets remain far less explored spectroscopically. Here, combining termination‐resolved micro‐ARPES, fine photon‐energy mapping, spin‐ARPES, and density functional theory, we map the three‐dimensional fermiology of the layered g ‐wave altermagnet , obtained by ordered Co intercalation of 2H‐. We resolve the spin–split branches of the altermagnetic pairs directly in the raw photoemission spectra and, with spin‐ARPES at these experimentally identified momenta, show the reversal of the spin polarization at opposite momenta and between two regions of the sample, consistent with opposite time‐reversal domains, and its absence along the symmetry‐protected nodal –K direction. We further report a weak low‐temperature anomaly near T 0 ≈ 50–60 K, detected by magnetometry, temperature‐dependent micro‐ARPES, and ultrafast reflectivity, whose microscopic origin remains open. These results provide a momentum‐resolved benchmark of the electronic structure of a layered altermagnet.

Advanced Materials
Boston College (US), Ulsan College (KR), Pohang University of Science and Technology (KR), University of Copenhagen (DK), Centre National de la Recherche Scientifique (FR), University of Salerno (IT), University of Trieste (IT), University of Trento (IT), Aarhus University (DK), University of Würzburg (DE), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), European Spallation Source (SE), Istituto Nazionale di Fisica Nucleare, Galileo Galilei Institute for Theoretical Physics (IT), Fritz Haber Institute of the Max Planck Society (DE), Synchrotron soleil (FR), Elettra-Sincrotrone Trieste S.C.p.A. (IT), Diamond Light Source (GB), CEA Grenoble (FR), ETH Zurich (CH), Superconducting and other Innovative Materials and Devices Institute (IT), Centre de Nanosciences et de Nanotechnologies (FR), Istituto Officina dei Materiali (IT), Institute for Basic Science (KR), Institute of Structure of Matter (IT), Federico II University Hospital (IT), Spintronique et Technologie des Composants (FR), Technische Universität Berlin (DE), Monash University (AU), AGH University of Krakow (PL), University of Naples Federico II (IT), Université Grenoble Alpes (FR)
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Magnetic properties of thin films
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