In most conventional materials, such as copper and silicon, electrons move about the

lattice independently, effectively ignoring each other. Despite some idiosyncrasies from

being an atomically thin layer of carbon, graphene is no exception to this behavior. If

we stack two sheets of graphene on top of each other, we might expect the composite

system would behave similarly to two copies of monolayer graphene. Remarkably, this

intuition is completely wrong.

If the two layers are stacked with a relative twist near one degree, they hybridize to

form new electronic bands with the remarkable property that all the electrons have

nearly the same kinetic energy. Freed to fill states in those bands without regard to

kinetic energy, electrons can collectively arrange themselves to minimize their mutual

Coulombic repulsion. This may explain the superconductivity surprisingly seen in such

stacks. Here, we will discuss the discovery that, despite containing none of the

traditional magnetic elements, twisted bilayer graphene can become magnetic. Unlike

conventional magnets, where magnetism arises from the ordering of electron spins,

twisted bilayer graphene’s magnetic state originates from perpetually swirling current

loops. Such "orbital magnetism" has now been seen in multiple different stacks of

atomically-thin materials.