Terahertz pulses hit a topological insulator
Terahertz pulses hit a topological insulator
Terahertz pulses (from left) hit a topological insulator. They excite the electrons, whose possible states are specified by energy bands. The bands inside the material (blue) are extended and have a large energy gap, which makes the material an electrical insulator here. The situation is completely different on the surface: the bands that form there (red) bridge the energy gap and ensure metallic behaviour. The experiment shows that the electrons in these surface states return to the equilibrium state very quickly (purple lattice). In contrast, it takes the electrons in the other bands about 10 times as much time to come to rest (yellow lattice).
