Imagine a spiral staircase with balls rolling down. Some are twisted to the right, others to the left. The steps are arranged so that right-twisted balls slip through faster, while left-twisted ones get stuck. Something similar happens inside helical molecules — for example, in the double helix of DNA. Electrons passing through it are divided into two types based on the direction of their internal rotation (spin). This phenomenon is called chirality-induced spin selectivity, or CISS. But until now, it was unclear how exactly the helix turns the random motion of electrons into a steady flow with a preferred spin.

The authors built a model: an electron jumps from a donor molecule through a DNA chain to an acceptor. Inside the helix, the electron experiences spin-orbit coupling, as if the geometry of the staircase itself gives a slight push to the balls depending on their rotation. But this push alone is not enough. The key role is played by dissipation — the process by which the electron loses energy, like a ball rubbing against the railing. The authors introduced a special condition: dissipation does not distinguish between spins, but its rate is tuned to 'freeze' the temporary advantage of one type of electron. Weak spin-orbit coupling creates only a tiny imbalance, and dissipation locks it in, turning it into a stable current polarization.

If you mentally flip the helix, make it a mirror image, the preferred spin direction also reverses. Thus, the molecule acts as a magnetic filter without any magnet. This mechanism is universal: it is not tied to a specific molecule and works due to dissipation, which is present in any medium. Understanding such processes opens the way to controlling spin currents in organic materials — a step toward future electronics where information is carried by electron spin rather than charge.