A piece of magnetite, an ordinary iron stone, behaves strangely. At room temperature, it conducts electricity, but cool it below minus 150 degrees, and its resistance jumps sharply. This jump, discovered back in 1939, physicists could not explain for nearly a century.

A new study offers a solution. The researchers built a computer model in which charge carriers are not free electrons but polarons: electrons 'dressed' in a cloud of crystal lattice vibrations. Such a particle is heavier than an electron and moves in jumps, like a person carrying a heavy backpack.

The model showed that the transition does not change the band structure — how electron energy depends on momentum. Instead, trimerons come into play: groups of three iron atoms that rearrange and begin to move. Previously, it was thought that the transition was linked to a change in band structure, but the calculations refute this.

The authors compared their model with experimental data on magnetite's conductivity at various temperatures. The match was excellent. This means that the Verwey mystery has finally been explained: the resistance jump is caused not by a change in electronic structure but by the collective motion of trimerons.