Electrons in graphene reach supersonic speeds for first time
Researchers have achieved a breakthrough by pushing electrons in graphene to supersonic speeds, creating a hydraulic jump similar to a sonic boom. This experiment, conducted using a microscopic nozzle, marks the first observation of such electron behavior. The findings could help resolve debates on electrically charged shockwaves.
For the first time, electrons have been made to flow so fast within graphene that they created a shockwave, mimicking fluid dynamics on a microscopic scale. In 2016, scientists first demonstrated electrons flowing like a viscous liquid in the ultra-thin carbon material graphene. Building on this, Cory Dean at Columbia University in New York and his colleagues engineered electrons to execute a hydraulic jump—a dramatic transition from fast to slow flow.
A hydraulic jump is familiar from everyday life, such as the ring-shaped boundary of fast and slow water under a running faucet. “In certain ways, it’s like a sonic boom going on in your kitchen sink,” says Doug Natelson at Rice University in Texas, who was not involved in the study.
To achieve this with electrons, the team constructed a microscopic nozzle from two layers of graphene, resembling the 19th-century de Laval nozzle used in rocket engines. This design pinches in the middle, allowing fluid to accelerate to supersonic speeds in the constriction and form a shockwave upon exiting. Unlike typical electron measurements that track current between device ends, the researchers adapted a microscope to map electron voltage across multiple points in the nozzle, enabling detection of the jump. Team member Abhay Pasupathy, also at Columbia University, highlighted this innovative approach.
Natelson emphasized the challenge: “there is art and finesse to making graphene structures pristine enough for electrons to be really ‘cheek by jowl’”—packed closely to enter this regime. Thomas Schmidt at the University of Luxembourg called the resolution of the microscopic jump technically impressive.
The experiment opens doors to probing long-standing questions about electrically charged shockwaves. Dean noted ongoing debate over whether the hydraulic jump emits radiation, potentially useful for generating infrared and radio waves. “Every experimentalist that we discuss this with is thinking about ways that you can detect this emission. Every theorist says there’s no way it’s going to emit anything. There’s a question there about what’s actually happening,” he said.
The research is detailed in arXiv DOI: 10.48550/arXiv.2509.16321.