An ordinary superconductor works like a perfect conductor: electrons pair up and flow without resistance. In the new material TaPtSi, the pairs are arranged differently: their internal symmetry is skewed, and when cooled below the critical temperature, tiny magnetic fields spontaneously emerge inside the crystal. It's as if invisible compass needles suddenly appeared in a frozen piece of metal, pointing in different directions.
The secret lies in the crystal's special geometry. Atoms in TaPtSi are arranged so that when the lattice is rotated or slid, it does not coincide with itself completely, but only when accompanied by a flip of the electron spin. This "twisted" symmetry creates hourglass-shaped nodes in the electronic structure: near their waists, the electron energy barely changes with motion. In these regions, electrons behave like relativistic particles with zero mass, even though the material itself is an ordinary solid alloy.
Calculations showed that this state is the only possible one for this structure. The electron pairs in it are not just glued together but twisted like a screw: their wave function carries an internal moment. On the surface of such a superconductor, special excitations, Majorana modes, can appear, which behave like halves of an electron. If they can be stabilized, they could become building blocks for quantum computing that is resistant to noise.
The discovery provides not just a new material but a recipe: take a compound of silicon with a transition metal, tune the lattice symmetry, and you get a topological superconductor. Perhaps this is how we will search for a platform for the future quantum computer.
Majorana modes are named after Ettore Majorana, who proposed a particle that is its own antiparticle. In superconductors, such excitations can be "halves" of ordinary electrons.
In Neal Stephenson's novel "Anathem," quantum computers use topological states of matter to avoid errors — much like Majorana modes in superconductors are protected from decoherence.