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Using the Multi-frequency High Field Electron Spin Resonance Spectrometer at the Steady-State High Magnetic Field Facility (SHMFF), researchers observed the first-ever Bose–Einstein condensation (BEC) of a two-magnon bound state in a magnetic material. The facility is in the Hefei Institutes of Â鶹ÒùÔºical Science of the Chinese Academy of Sciences and includes a research team from Southern University of Science and Technology, Zhejiang University, Renmin University of China, and the Australian Nuclear Science and Technology Organization.

This discovery was in Nature Materials.

BEC is a fascinating quantum phenomenon where particles, typically bosons, condense into a single collective state at ultra-low temperatures. While this effect has been seen in cold atoms, it had never been observed in a magnetic system until now.

In this study, the researchers focused on magnons—quanta of spin excitations—and discovered that pairs of magnons could bind together and form a condensed state, similar to BEC in atoms.

The material at the heart of this discovery is Na₂BaNi(PO₄)₂, a quantum magnetic compound with a unique triangular lattice structure. This structure makes it a perfect candidate for studying frustrated quantum magnetism—a state where spins of electrons behave in strange, unpredictable ways due to competing interactions.

This discovery differs from conventional superconductivity, which involves pairing fermions. Instead, the team uncovered a unique form of magnon pairing that leads to a quantum phase transition, offering fresh insights into exotic quantum states of matter.

SHMFF allowed them to detect minuscule signals corresponding to two-magnon bound states, which matched theoretical predictions. Their experiments also included low-temperature thermodynamics, neutron scattering, and nuclear magnetic resonance techniques, further confirming the existence of the magnon BEC.

This achievement paves the way for deeper exploration of quantum materials, potentially unlocking new phases of matter that could be harnessed in future technologies, according to the team.