Hidden within thin layers of tantalum selenide (TaSe₂) is a property that defies conventional physics. When guest atoms were added between the layers of this material, the structure lost its center of symmetry, and inside, superconductivity with armor emerged. Normally, a strong magnetic field destroys the superconducting state by breaking electron pairs. Here, however, the critical field directed along the layers turned out to be anomalously large: it exceeded the so-called Pauli limit (the theoretical maximum for a conventional superconductor).

The secret lies in spin polarization. Electronic structure calculations showed that electron spins are rigidly tied to the direction of motion and oriented perpendicular to the layers. This is like a translator who gets distracted by every rustle in the room, and a one-hour meeting stretches into two. Here, too: spin-orbit interaction locks the spins, preventing the magnetic field from flipping them. As a result, pairs survive where they should have fallen apart.

Experiments with different material thicknesses and measurements of the superconducting diode effect (where current flows more easily in one direction than the opposite) confirmed that we are dealing with so-called Ising superconductivity. And not in a monolayer, but in a bulk sample — which is rare. As thickness decreased, the ratio of the critical field to the Pauli limit changed, revealing details of how the protection evolves with the number of layers.

Thus, the layered crystal turns into a platform for studying exotic quantum states. And the resilience to magnetic fields is a step toward superconducting electronics, where the direction of current can be controlled without losses.