Imagine a carousel with two types of seats: some spin clockwise, others counterclockwise. If you push all of them at once, the carousel jerks but stays in place. That's how a Weyl semimetal crystal works: electrons are born in pairs—'left' and 'right'—and their contributions to current cancel each other, like two identical motors running in opposite directions.

Physicists have found a way to push only one type of seat. Two laser pulses are sent into the crystal simultaneously. The first is circularly polarized, as if the beam draws a spiral. The second is linearly polarized, like a straight line, but at twice the frequency. These two pulses are tightly locked in phase: their crests and troughs always move in the same rhythm. Together, they create a field in the material that acts differently on left- and right-handed electrons. One type gains energy and starts moving, the other doesn't. A pure current emerges.

The most intriguing part is that the current can be controlled simply by adjusting the delay between the two pulses or their intensities. Slightly shift the phase, and the current flows in the opposite direction. It's like adjusting the volume and direction of sound in headphones: you don't touch the speakers themselves, only the input signal. The authors calculated that at a certain ratio of the strengths of the two colors, selectivity becomes maximal — almost all excited electrons are of one type. Such optical control of charge dynamics opens the way to ultrafast electronics, where signals are switched not by voltage but by light. Then the carousel can be set in motion without extra pushes, just with a precise move.