Fast Electrons Tie Quantum Knots

摘要

Objects traveling near the speed of light bring space travel to mind, but in familiar solids containing heavy elements (such as in a gold ring), the velocities of electrons are high enough that effects arising through special relativity come into play. The main effect for electrons is that the orientation of their spins depends on their trajectories. This effect, called spin-orbit coupling, seemed to be understood thoroughly by the 1960s, butrnnew theoretical and experimental studies are driving its revival. Two reports in this issue discuss how spin-orbit coupling causes novel forms of electronic organization that can be captured by topology, the branch of mathematics that classes objects on the basis of properties that do not change upon deformation (and so lumps coffee cup handles together with doughnuts).