The stacking of graphene layers creates a fabric that may carry electrical energy with out resistance and behave like a magnet at chilly temperatures.
Credit:Picture credit score: Sampson Wilcox, Analysis Laboratory of Electronics
Graphite is fabricated from layers of graphene—single-atom-thick, lattice-like sheets of carbon atoms—which can be stacked and may simply flake off beneath stress, reminiscent of when writing on paper. A single graphite flake can maintain tens of millions of graphene layers, often aligned so each different layer matches. Nonetheless, some areas have a special stacking sample, forming a staircase-like construction. Researchers at MIT discovered that when 4 or 5 graphene layers are stacked on this “rhombohedral” means, the fabric exhibits distinctive digital properties not present in common graphite.
Of their examine, the physicists remoted flakes of rhombohedral graphene from graphite and ran electrical exams. They discovered that when the flakes are cooled to 300 millikelvins (about -273 levels Celsius), the fabric turns into a superconductor, permitting electrical present to circulate with out resistance.
In addition they discovered that altering an exterior magnetic discipline up and down may change the flakes between two superconducting states, just like a magnet. This means the superconductor has inside magnetism. This switching will not be present in different superconductors.
The researchers examined how this new superconducting state reacts to an exterior magnetic discipline. They utilized a magnetic discipline and a voltage to the fabric and measured the ensuing electrical present. As they different the magnetic discipline from adverse to constructive polarity and again, they noticed that the fabric stayed in its superconducting, zero-resistance state, besides at two factors—one at every magnetic polarity. At these factors, the resistance briefly elevated earlier than dropping again to zero, and the fabric returned to its superconducting state.
The researchers noticed the identical uncommon habits in six samples and consider it’s because of the particular stacking of rhombohedral graphene. At very chilly temperatures, electrons decelerate and begin interacting. These interactions make electrons pair up and transfer with out resistance—that is superconductivity.
On this materials, electrons all transfer in the identical route, or “valley,” so once they pair up, their movement doesn’t cancel out. This creates superconducting pairs with spin, which collectively can produce built-in magnetism.
