“The idea of “two-dimensional matter” is foreign to me.”
Graphine is a single atom thick, and I’ve seen people referring to it as two-dimensional, but even a single atom is three-dimensional, isn’t it?
“but even a single atom is three-dimensional, isn’t it?”
Not really. If the “height” is one atom high then that dimension is so small to be almost negligible. For practical purposes it is two dimensional.
Correct! Any material thing that occupies space has 3 dimensions. It just seemed incongruous for a learned article to use “two-dimensional” when referring to this material.