In a three-story building made of nickel and oxygen, two residents are missing. Physicists call these vacant spots holes, and where they sit determines whether the material becomes a superconductor — a lossless conductor.
Quantum mechanics describes such holes as real particles with positive charge. In the normal state, one hole is locked in the middle floor, while the other hangs between floors. Current can't push through.
Computer calculations showed that upon compression, the holes relocate to the outer layers and form pairs that carry current without resistance. It's as if the residents moved from the middle of the house to wings on the sides, and seamless communication was established between them.
Thus, the three-layer nickelate La4Ni3O10 mimics the behavior of its two-layer relative La3Ni2O7, where superconductivity under pressure has already been observed experimentally.
A hole is not just the absence of an electron. It behaves like a particle with positive charge and its own mass, and can carry current just as well as electrons.