MARCH 24, 2026 -- A team of scientists led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory have identified a rare, switchable quantum property in a new type of nickel sulfide material. The discovery could have applications in high-speed transistors, adaptive sensors and other devices that require a material’s electronic structure to be controlled on the fly.

The compound, KxNi₄S₂ (0 ≤ x ≤ 1), contains nickel and sulfur sandwiched between layers of potassium. The “(0 ≤ x ≤ 1)” in the name means that the amount of potassium in the material can vary from no potassium at all to a full potassium atom, depending on the sample. First detailed in a 2021 paper, it was created as part of an ongoing quest to develop more superconductors. As researchers examined the layered material’s characteristics, they happened upon a remarkable feature: Applying an electrical current could drive the potassium layers out, collapsing the sandwich and changing the material’s structure. This action, which is reversible, allows the one material to host two different types of quantum features: Dirac cones and flat band systems.

“You can tune how much potassium comes out of the material, from full to empty and everything in between. This means you can switch from one quantum state to another, all within the same material,” said Mercouri Kanatzidis, a professor at Northwestern University with a joint appointment as a materials scientist at Argonne, who led the research. ​“I cannot name another material that can do this — if one exists, it is not well known.”

Key Argonne contributors to the work with Kanatzidis included Duck Young Chung, principal materials scientist; Hyowon Park, a joint appointee at the University of Illinois at Chicago; and postdoctoral researchers Hengdi Zhao and Xiuquan Zhou. Zhou is now an assistant professor at Georgetown University.

Dirac cones and flat bands can function as traffic controllers for electrons, which are negatively charged subatomic particles. Electrons in a Dirac cone appear light and can move very fast; in a flat band, the same electrons will seem massive and slow down. The researchers created samples of the material at Argonne’s Center for Nanoscale Materials (CNM) and calculated its electronic structure using the Bebop high-performance computing cluster at Argonne’s Laboratory Computing Resource Center. They verified the dual states in KxNi₄S₂ (0 ≤ x ≤ 1) by observing samples at the Advanced Photon Source (APS). Both CNM and APS are DOE Office of Science user facilities.

This is not the first unexpected discovery to arise from superconducting materials research by Kanatzidis and colleagues. Another compound originally designed as a potential superconductor proved ineffective for that purpose but turned out to be an excellent candidate for batteries and other energy conversion technologies. Kanatzidis has also studied halide perovskites for next-generation photovoltaics, work for which he recently received the 2026 William H. Nichols Medal from the American Chemical Society.

The end goal of the fundamental science that creates these new compounds is to discover new quantum materials and superconductors. Each step is yielding important insights, such as a new method for discovering and making crystalline materials with two or more elements. This was the method used to make KxNi₄S₂ (0 ≤ x ≤ 1).

“The high amount of nickel in this material means the nickel atoms have to interact and bind to each other, and that’s what we think gives rise to its interesting properties,” Kanatzidis said. ​“We have a much better understanding of what gives rise to this type of compound, and now we want to generalize our synthesis method to find more materials just like it.”

Funding for the research came from DOE’s Office of Science, Argonne National Laboratory, the National Science Foundation, Georgetown University and DOE’s National Nuclear Security Administration.