An international team of researchers has discovered a previously unrecognized magnetic state in a material composed of four atomic layers of chromium iodide. Dr. Ruoming Peng, a postdoctoral researcher at the 3rd Physics Institute of the University of Stuttgart, noted that the team successfully fine-tuned the magnetism by manipulating electron interactions within each layer. Alongside doctoral researcher King Cho Wong, Peng conducted the experiments at ZAQuant. "By adjusting the interactions between electrons in the individual layers, we can selectively control this magnetism," he explains. "Notably, the magnetic properties observed are resilient against environmental disturbances."
Twisted 2D Materials Generate Skyrmions
Chromium iodide is classified as a two-dimensional (2D) material, consisting of only a few atomic layers arranged in a crystalline form. These ultra-thin materials exhibit behaviors that significantly differ from their thicker, three-dimensional counterparts.
In their study, the researchers slightly rotated two stacked bilayers of chromium iodide in relation to each other. This minor twist resulted in the emergence of a groundbreaking magnetic configuration. "In contrast, a bilayer without twist does not present a net external magnetic field, as previous studies have shown," says Peng. The rotation facilitates the formation of skyrmions, which are nanoscale magnetic structures that are topologically protected and remarkably stable. They are recognized as some of the smallest and most durable information carriers in magnetic systems. For the first time, the team successfully generated and directly observed skyrmions within a twisted two-dimensional magnetic material.
Quantum Sensing Reveals Subtle Magnetism
Detecting this new magnetic state posed challenges due to the extremely weak signals involved. To measure them, the scientists utilized an advanced microscope employing quantum sensing techniques. This method leverages nitrogen-vacancy (NV) centers in diamond, a technology that has been honed at the Center for Applied Quantum Technologies over the past two decades.
Findings Redefine Magnetic Theory
This discovery not only opens new avenues for high-density data storage but also enhances our understanding of collective electron behavior in atomically thin magnetic systems. "Our experimental findings suggest that current theoretical models must be refined to accurately reflect the observed phenomena," states Wrachtrup.
The project involved collaboration among researchers from the United Kingdom, Japan, the United States, and Canada, in addition to the University of Stuttgart. The University of Edinburgh led the theoretical modeling and numerical simulations.
About the Center for Applied Quantum Technologies
The Center for Applied Quantum Technologies (ZAQuant) focuses on research and education in solid-state quantum technology, with applications ranging from nanoscale quantum sensing to quantum networks. The institute boasts a unique combination of precision and quantum optics laboratories, along with state-of-the-art cleanroom facilities.