A jar lid is easier to twist when you grip the rim rather than the center. Layered materials behave in much the same way when you try to rotate one layer relative to another: the resistance comes not from the whole contact area but only from its edge.
Previously, it was thought that the resistance to twisting should grow in proportion to the square of the contact area, since a circular contact twice as large contains four times as many atoms. But measurements showed that the torque grows linearly. This means the inner regions of the contact barely resist at all.
Atomistic simulations explained why: at the edges of the contact, the atomic lattice rearranges to lower its energy, and it is this narrow strip that bears the brunt of the load. The inner part remains largely uninvolved, like the middle of a lid that you cannot get a grip on. This finding helps in designing microdevices where layers need to be rotated with precision.
The torque for graphite on graphite at a radius of 2 μm was about 40 nN·m, comparable to the torque produced by an ant turning a blade of grass 1 mm long.
In Arthur C. Clarke's novel 'Childhood's End,' aliens use technology that allows manipulation of materials at the atomic level. This work on controlled twisting of layers resembles the first steps toward such capabilities.