Superconductivity can be switched on and off in “magic-angle” graphene using a short electrical pulse, according to new work by researchers at Massachusetts Institute of Technology (MIT). Until now, such switching could only be achieved by sweeping a continuous electric field across the material. The new finding could help in the development of novel superconducting electronics such as memory elements for use in two-dimensional (2D) materials-based circuits.

Graphene is a 2D crystal of carbon atoms arranged in a honeycomb pattern. Even on its own, this so-called “wonder material” boasts many exceptional properties, including high electrical conductivity as charge carriers (electrons and holes) zoom through the carbon lattice at very high speeds.

In 2018, researchers led by Pablo Jarillo-Herrero of MIT found that when two such sheets are placed on top of each other with a small angle misalignment, things become even more fascinating. In this twisted bilayer configuration, the sheets form a structure known as a moiré superlattice, and when the twist angle between them reaches the (theoretically predicted) “magic angle” of 1.08°, the material begins to show properties such as superconductivity at low temperatures – that is, it conducts electricity without any resistance.

Researchers at Harvard University, the Lawrence Berkeley National Laboratory, Arizona State University, and other institutes in the United States have recently observed an antiferromagnetic metal phase in electron-doped NdNiO₃ a material known to be a non-collinear antiferromagnet (i.e., exhibiting an onset of antiferromagnetic ordering that is concomitant with a transition into an insulating state).

“Previous works on the rare-earth nickelates (RNiO₃) have found them to host a rather exotic phase of magnetism known as a ‘noncollinear antiferromagnet,’” Qi Song, Spencer Doyle, Luca Moreschini and Julia A. Mundy, Four of the researchers who carried out the study, told Phys.org.

“This type of magnet has unique potential applications in the field of spintronics, yet rare-earth nickelates famously change spontaneously from being metallic to insulating at the exact same temperature that this noncollinear antiferromagnet phase turns on. We wanted to see if we could somehow modify one of these materials in a way so that it remained metallic, but still had this interesting magnetic phase.”

Physicists at the University of Wisconsin-Madison have directly measured the fluid-like flow of electrons in graphene at nanometer resolution for the first time. The results appear in the journal Science today.

Graphene, an atom-thick sheet of carbon arranged in a honeycomb pattern, is an especially pure electrical conductor, making it an ideal material to study electron flow with very low resistance. Here, researchers intentionally add impurities at known distances, and find that electron flow changes from gas-like to fluid-like as the temperature rises.

“All conductive materials contain impurities and imperfections that block electron flow, which causes resistance. Historically, people have taken a low-resolution approach to identifying where resistance comes from,” says Zach Krebs, a physics graduate student at UW-Madison and co-lead author of the study. “In this study, we image how charge flows around an impurity and actually see how that impurity blocks current and causes resistance, which is something that hasn’t been done before to distinguish gas-like and fluid-like electron flow.”