Key Findings
A collaborative research team from Cornell University, Stanford University, the University of Illinois Urbana-Champaign, Stony Brook University, and Japan’s National Institute for Materials Science (NIMS) has shown that an electric field can switch four-layer graphene between nonmagnetic and magnetic states. Crucially, the material remains in the switched state even after the voltage is removed, indicating a persistent structural change.
Technical Details
The switching mechanism involves sliding the layers of graphene into different stacking arrangements. The researchers utilized gate voltages to drive a transition between two primary states:
- Bernal stacking: The most stable arrangement, which is nonmagnetic.
- Rhombohedral stacking: A less stable arrangement that hosts correlated and topological phases, including magnetism and superconductivity.
Using transport measurements on marginally twisted double-bilayer graphene samples, the team observed bistable switching between a Bernal-dominated state and a mixed rhombohedral–Bernal state across a wide range of gate voltages. This transition corresponds to a switch between a nonmagnetic and a ferromagnetic phase. At low temperatures, the ferromagnetic phase exhibits an anomalous Hall effect, with a signal that reverses sign when the displacement field is reversed, suggesting the effect originates from the boundaries between the Bernal and rhombohedral domains.
Significance and Outlook
The ability to reliably switch the structure back and forth suggests that this effect can serve as a reliable memory source. Lead author Daniel Brandon noted that once the material enters a specific state, it persists for a long time. Senior author Kenji Yasuda indicated that this technique provides a route to materials whose properties can be rewritten on demand. Beyond magnetism, the researchers suggest that electrically rewriting the structure may enable the switching of superconductivity and other quantum states, pointing toward the development of reconfigurable quantum materials and new forms of nonvolatile memory.
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