Inside a superconductor, a magnetic field typically twists into tubes, vortices, each carrying one quantum of magnetic flux. That's how the classic Abrikosov lattice works. But in LiFeAs crystals, the picture is different.

Muon spectroscopy showed that the field penetrates not as individual vortices but as stripes. Each stripe contains pairs of 'coreless' vortices. These are bound states of two half-quantum vortices separated in space. So instead of a single tube with a whole flux quantum, you get two halves separated by a field-free region.

Such a structure indicates an unusual superconducting state in LiFeAs. Possibly, the material has several competing order parameters, and under certain conditions they form a striped phase. This discovery helps better understand the mechanisms of superconductivity in iron-based compounds.