When Dr. Jaime Sánchez-Barriga and his team at Berlin's Helmholtz-Zentrum Berlin pointed their advanced spectroscopy equipment at cobalt, one of Earth's most familiar metals, they expected to confirm what scientists had believed for four decades: that cobalt's electronic structure was thoroughly understood. Instead, they found a hidden quantum world sprawling inside.
Using spin- and angle-resolved photoemission spectroscopy at the BESSY II synchrotron radiation facility, the international research team discovered that cobalt contains a rich network of topological electronic states—special configurations of electrons that remain stable even at room temperature. The findings challenge fundamental assumptions about this elemental metal and suggest it could become central to the next generation of electronic and spin-based technologies.
What makes this discovery remarkable is the sheer density and strangeness of what the researchers found. Cobalt's electronic structure is dominated by what physicists call magnetic nodal lines: special topological band crossings where two spin-polarized electronic states intersect continuously without forming an energy gap. Rather than appearing at isolated points, these crossings extend along paths throughout the crystal in what Sánchez-Barriga describes as "numerous crossings and nodes that dominate its low-energy electronic behavior."
Even more striking, near these crossings, electrons in cobalt behave like massless, relativistic particles—similar to how light behaves—allowing them to travel at exceptional speeds. This is behavior that had never been observed in any elemental ferromagnet before. "In certain directions inside the crystal, the nodal lines intersect and cross the Fermi energy where electrons can move freely," Sánchez-Barriga explains. "Near these crossings, electrons in the material behave like massless, relativistic-like particles, similar to how light behaves, and can travel extremely fast."
What makes cobalt particularly valuable for future technologies is that these electronic states can be directly controlled using magnetic fields. Because cobalt is ferromagnetic—meaning it breaks the symmetry of time—the electronic states linked to the nodal lines carry a net spin polarization. Crucially, this spin polarization can be completely reversed by changing the direction of the material's magnetization. This provides direct magnetic control over the charge carriers, a capability that does not exist in non-magnetic nodal-line materials and is exactly what spintronics researchers have been seeking.
"Magnetic nodal-line materials are rare in nature, and in most known cases such crossings are extremely difficult to stabilize or control," Sánchez-Barriga says. "The observation of multiple symmetry-protected nodal lines in a simple elemental ferromagnet is therefore highly unexpected and establishes cobalt as a model system for studying the interplay between topology and magnetism."
The theoretical team led by Dr. Maia G. Vergniory of the Donostia International Physics Center and Université de Sherbrooke confirmed these experimental results through first-principles calculations, successfully identifying all the nodal lines in cobalt's bulk electronic structure and showing excellent agreement with measurements. The analysis revealed that the nodal lines are protected by crystalline mirror symmetries working together with ferromagnetism.
Looking forward, the researchers believe this discovery may point to similar hidden topological features lurking inside other elemental and transition-metal ferromagnets. If confirmed, cobalt could serve as a blueprint for unlocking quantum properties in materials scientists once thought they fully understood—opening doors to devices that seamlessly control both charge and spin in ways previously impossible.