Two dancers on one stage: one pulls one way, the other pulls the opposite. In the crystal Cu2(OH)3Br, copper atoms line up in chains, and their magnetic moments (spins) can align in different ways: sometimes parallel, sometimes antiparallel. It is like a single dance that combines moves in unison and in opposite phase. Scientists wanted to understand how an external magnetic field rearranges this dance.

The scientists applied magnetic fields up to 31 tesla (a million times stronger than Earth's field) and watched how the crystal absorbed terahertz radiation. When the field was directed perpendicular to the chains, at 5.4 tesla the spins flipped abruptly: some modes disappeared, and others appeared. When the field was directed along the chains, there was no abrupt flip, but at 16.3 tesla one subsystem completely froze, leaving only a single broad mode.

This made it clear: previously, it was unknown how coexisting magnons and spinons exchange energy as the field changes. Now it is evident that the field acts like a conductor: it either sharply changes the dance or smoothly sidelines one of the dancers. This is pure knowledge with no applications yet, but it helps understand how quantum magnets are organized.