Light plays a vital role in our everyday lives, and technologies based on light are all around us. So we might expect that our understanding of light is pretty settled. But scientists have just uncovered a new fundamental property of light that gives new insight into the 150-year-old classical theory of electromagnetism and which could lead to applications manipulating light at the nanoscale.
It is unusual for a pure-theory physics paper to make it into the journal Science. So when one does, it’s worth a closer look. In the new study, researchers bring together one of physics’ most venerable set of equations—those of James Clerk’s Maxwell’s famous theory of light—with one of the hot topics in modern solid-state physics: the quantum spin Hall effect and topological insulators.
To understand what the fuss is about, let’s first consider the behavior of electrons in the quantum spin Hall effect. Electrons possess an intrinsic spin as if they were tiny spinning-tops, constantly rotating about their axis. This spin is a quantum-mechanical property, however, and special rules apply—the electron has only two options open to it: it can either spin clockwise or counterclockwise (conventionally called spin-up or spin-down), but the magnitude of the spin is always fixed.
