Researchers unlock hidden pathway to tunable magnetic devices

A new study published in Nature Communications April 7 could reshape the future of magnetic and electronic technology. Scientists at Rice University have discovered how a disappearing electronic pattern in a quantum material can be revived under specific thermal conditions. The finding opens new doors for customizable quantum materials and in-situ engineering, where devices are manufactured or manipulated directly at their point of use.

Led by Pengcheng Dai, the Sam and Helen Worden Professor of Physics and Astronomy, the researchers uncovered the cause behind a vanishing electronic phenomenon in a class of crystalline materials known as kagome lattice, a geometric arrangement of corner-sharing triangles named after a traditional Japanese basket pattern. This discovery reveals how heating methods impact the presence of a charge density wave (CDW), a quantum pattern of electron arrangement, in the kagome metal iron germanide (FeGe). It also demonstrates how its reappearance enhances magnetic and electronic properties.

“Our study brings us closer to developing in-situ controllable quantum materials,” Dai said. “By identifying how structural defects drive or suppress these electronic patterns under different annealing conditions, we now understand how to manipulate magnetism and conductivity in ways that can inform the next generation of magnetic sensors.”

Engineering with electrons

The study zeroed in on the kagome lattice FeGe, known for giving rise to an unusual electronic pattern called a CDW below 100 degrees Kelvin. The structure in FeGe presented a puzzling behavior: Its CDW and associated lattice distortions would vanish if the sample was annealed at high temperatures only to reemerge more strongly when the material was reheated at a lower temperature. This annealing-dependent CDW order is extremely rare in quantum materials, Dai said.

To uncover why, researchers conducted repeated thermal cycles while employing high-resolution scanning transmission electron microscopy to monitor structural changes. Using neutron scattering, they observed magnetic behavior tied to CDW presence, while Hall effect measurements provided insights into how electron flow shifted under a magnetic field in the same sample with and without CDW order obtained under different annealing conditions.

Through this multifaceted approach, the team was able to correlate atomic-level defects to macroscopic quantum behaviors, showing how the microstructure of a material dictates its broader electronic and magnetic properties through the annealing process.

A defect with a purpose

The breakthrough came with the identification of atomic vacancies in germanium. High-temperature annealing treatment caused these atoms to escape, leaving evenly spaced holes. At lower temperatures, however, the vacancies began clustering into extended regions, conditions that stabilized the long-range CDW pattern.

Simultaneously, researchers detected the emergence of two distinct magnetic orders, one closely intertwined with the reestablished CDW. Most notably, the material’s ability to conduct electrons in a magnetic field surged by a factor of 10 when the CDW returned.

“Our results not only explain a long-standing mystery but also highlight the potential of kagome materials for in-situ novel sensors and quantum devices through a simple annealing process,” said Mason Klemm, a Rice graduate student and first author of the study.

By demonstrating how to control CDW behavior through thermal tuning and defect engineering, the study lays the groundwork for precision-designed materials with on-demand electronic and magnetic properties.

“This is just the beginning,” Dai said. “With this knowledge, we can start designing materials that behave exactly how we want.”

Co-authors of this study include Sijie Xu, Yaofeng Xie, Tanner Legvold, Xiaokun Teng, Bin Gao, Douglas Natelson and Ming Yi of the Department of Physics and Astronomy at Rice; Saif Siddique, Judy J. Cha and Mehrdad T. Kiani of Cornell University; Yuan-Chun Chang and Chien-Lung Huang of National Cheng Kung University; Feng Ye, Huibo Cao, Yiqing Hao, Wei Tian and Masaaki Matsuda of Oak Ridge National Laboratory; and Hubertus Luetkens and Zurab Guguchia of the Paul Scherrer Institute’s Center for Neutron and Muon Sciences.

The U.S. National Science Foundation and the Robert A. Welch Foundation supported this study.