In some crystals, electrons are not distributed evenly but alternate: one atom has more, the neighboring one has fewer. The result is a pattern resembling a chessboard. Such a pattern is called charge order. It was once thought to be static, but recently it turned out that an electric field can flip it, just as a current flips magnetic order. The only remaining question was how exactly the field does this.
Physicists came up with a simple way to describe the situation. Each atom in the crystal can be either empty or occupied by two electrons at once. These two states were labeled with an arrow pointing up or down, and the label was called a pseudospin (not a real spin, just a convenient tag). In this description, charge order looks like an antiferromagnet: arrows on neighboring atoms point in opposite directions. And the electric field acts on these arrows as if pulling them in different directions.
This discovery makes it possible to control charge order with an electric field. Previously, this was not possible because there was no theory linking the field to the switching of the pattern. Now charge order can be used for storing and processing information, much like magnetic bits are used today.
The frequency of collective pseudospin excitations of charge order lies in the terahertz range, that is, about a trillion oscillations per second. This is a million times faster than the typical frame rate in movies.