Researchers at the Institute of Physics in Zagreb, members of the Group for Complex and Strongly Correlated Functional Materials, working with collaborators from Croatia, Italy, Austria, and Poland, have solved a long-standing puzzle in the physics of two-dimensional magnetic materials. Using a synchrotron-based imaging technique called angle-resolved photoemission spectroscopy (ARPES), the team examined Co1/3TaS2, a layered material in which cobalt atoms are inserted between sheets of tantalum disulfide, giving rise to magnetism and unusual electrical behavior.
The measurements revealed a shallow electron “pocket” – dubbed the β (beta) feature – sitting right at the Fermi level, the energy threshold that governs how electrons move and conduct. This feature had been glimpsed before in related materials, but its origin was hotly debated: was it a genuine bulk property, or merely an artifact of the material’s surface?
Standard theoretical methods, even fairly sophisticated ones, could not reproduce the β feature at all. To crack the puzzle, the team turned to a more powerful approach called cluster perturbation theory, which treats the strong quantum interactions between electrons on the cobalt atoms far more rigorously than conventional methods. This approach successfully reproduced the elusive electron pocket, demonstrating that it emerges from strong electron correlations deep within the bulk of the material, rather than from its surface.
The results, published in Physical Review B, deepen our understanding of how magnetism, electron correlation, and electronic structure intertwine in cobalt-intercalated dichalcogenides – materials increasingly seen as promising building blocks for future spintronic and magnetoelectric devices.
The work was carried out mostly at the Institute of Physics, with the assistance of beamline scientists at the Elettra synchrotron in Trieste and theoretical support from Prof. Ivo Batistić of the Department of Physics, Faculty of Science, University of Zagreb. We would especially like to thank our colleague Eduard Tutiš for valuable discussions, Mario Novak and Neven Barišić for their long-standing collaboration in crystal synthesis and rigorous characterization, and Trpimir Ivšić for his effort invested in the synthesis.
The details of the work are available at: doi.org/10.1103/6y9w-lx94