Topological insulators are one of the most puzzling quantum materials—a class of materials whose electrons cooperate in surprising ways to produce unexpected properties. The edges of a TI are electron superhighways where electrons flow with no loss, ignoring any impurities or other obstacles in their path, while the bulk of the material blocks electron flow.
Source:
https://phys.org/news/2021-02-hands-off-probe-explore-electron-behavior.html