Spin-ARPES at BESSY II

To investigate these phenomena, the team employed spin- and angle-resolved photoemission spectroscopy (spin-ARPES) at BESSY II. This advanced method enables researchers to examine the energy and momentum of electrons while simultaneously measuring their spin orientation. The experiments uncovered an intricate network of magnetic nodal lines—topological band crossings where two spin-polarized electronic states intersect continuously without opening an energy gap.

Figure 1. Hidden Quantum Phenomena Discovered in an Everyday Element.

Rather than occurring at discrete points, these crossings form extended pathways throughout momentum space within the crystal. These features give rise to high-mobility, topologically protected charge carriers, making them highly attractive for future electronic and spintronic applications. Figure 1 shows Hidden Quantum Phenomena Discovered in an Everyday Element.

Cobalt as a Model System

A key feature of cobalt’s nodal lines is their intrinsic spin polarization. Since ferromagnetism breaks time-reversal symmetry, the electronic states that form these nodal lines possess a net spin orientation. When the magnetization direction of the material is reversed, this spin polarization can be completely flipped.

This property allows direct magnetic control over the charge carriers associated with the nodal lines—an essential capability for spintronic applications. Such tunable spin control is absent in non-magnetic nodal-line materials.

As Sánchez-Barriga explains, magnetic nodal-line materials are exceptionally rare, and in most previously identified systems, stabilizing or manipulating these crossings has been extremely challenging. The discovery of multiple symmetry-protected nodal lines in a simple elemental ferromagnet like cobalt is therefore unexpected and positions it as an ideal platform for exploring the relationship between topology and magnetism.

Experimental Results Consistent with DFT

These calculations demonstrate strong predictive capability by identifying all nodal lines within the computed bulk band structure simultaneously. The theoretical results align closely with the experimental data, confirming that cobalt’s nodal lines are protected by crystalline mirror symmetries in combination with ferromagnetism. Notably, the band crossings remain gapless even when spin–orbit coupling is taken into account.

Magnetic Switching Enables Control

Sánchez-Barriga explains that along specific crystallographic directions, the nodal lines intersect and cross the Fermi energy—the level at which electrons are free to move. Near these crossing points, electrons behave like massless, relativistic particles, similar to photons, allowing them to travel at exceptionally high speeds. This type of behavior has never before been observed in an elemental ferromagnet.

Importantly, adjusting the direction of the magnetic field enables researchers to either open an energy gap at the crossing points or precisely manipulate the spin texture of the nodal lines, all while preserving the distinctive properties of the gapless state. This magnetic tunability provides the kind of on–off switching functionality that is highly desirable for real-world electronic and spintronic devices.

Beyond potential applications, the researchers propose that comparable topological characteristics may also be present in other elemental and transition-metal ferromagnets. This possibility opens new pathways for uncovering exotic quantum phenomena in well-known materials. They also suggest additional strategies for tailoring these properties, such as investigating interfaces with high atomic-number materials or examining systems with reduced dimensionality.

Key Takeaways

This discovery highlights that our understanding of ferromagnetic metals is still evolving. Even widely studied magnetic elements can host previously hidden and unconventional quantum states. The findings point toward promising new research directions in magnetism, topological phases of matter, and their associated excitations.

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2026), Scientists Uncover Unexpected Quantum Behavior in a Common Element, AnaTechMaz, pp.446