Matter 9, 2026, 1, 102418
DOI: 10.1016/j.matt.2025.102418
Researchers from Argonne National Laboratory, Georgetown University, and collaborating institutes performed single-crystal X-ray diffraction at NSF’s ChemMatCARS, Sector 15 at the Advanced Photon Source (APS), Argonne National Laboratory, unveiling a layered nickel sulfide, KₓNi₄S₂ (0≤x≤1), whose electronic structure can be toggled between massless Dirac cones and flat-band heavy-electron states simply by electrochemically removing potassium. Results show that the intact compound, KNi₄S₂ (x=1), behaves as a non-magnetic topological Dirac metal, whereas full K deintercalation drives it to Ni₄S₂ (x=0), a flat-band-induced antiferromagnet, providing a single material platform for the first time in which the Fermi surface can be swept continuously from Dirac-fermion to flat-band dominance. The work identifies Ni-Ni bonding as the origin of the Dirac cones despite the absence of the usual Kagome or honeycomb lattice, and it establishes potassium intercalation/deintercalation as a practical “knob” for in-situ control of quantum ground states in layered materials.
https://www.sciencedirect.com/science/article/pii/S2590238525004618
