At a temperature of 4.3 degrees above absolute zero, a crystal of palladium telluride stops resisting electric current. Electrons pair up and move without loss, like a crowd holding hands. But this superconductor seems to have not one but two different ways of pairing.

Physicists pressed a sharp needle against the crystal and measured how current flows through the contact. The resulting curves did not fit a single energy gap. The data were best described by a model with two gaps: the larger gap takes about 3.7 units of thermal energy, while the smaller one ranges from 1.1 to 2.2. The coupling between electrons in these two groups is weak, so they barely interfere with each other.

Different contacts gave slightly different results. Most likely, the crystal surface is inhomogeneous: in some regions electrons form pairs with higher binding energy, in others with lower. This is like a terrain map where valleys and hills have different weather. Such "two-gap" superconductivity is rare and indicates a complex arrangement of electronic orbitals in PdTe.

A crystal with two gaps is like a house with two different locks on the front door. To understand who enters, you need keys to both. Physicists are just starting to pick them.