February 25, 2025 -- A first-ever discovery of Bose-Einstein condensation (BEC) in a two-magnon bound state has been achieved by a collaborative research team from Southern University of Science and Technology, Zhejiang University, Renmin University of China, and the Australian Nuclear Science and Technology Organization.

The observation was made using the Multi-frequency High Field Electron Spin Resonance Spectrometer at the Steady-State High Magnetic Field Facility (SHMFF) in Hefei Institutes of Physical Science of the Chinese Academy of Sciences.

The findings were published in Nature Materials.

BEC is a 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.

This effect was observed in Na₂BaNi(PO₄)₂, a quantum magnetic compound characterized by its unique triangular lattice structure. This material serves as an ideal platform for studying frustrated quantum magnetism, where electron spins behave in complex and unpredictable ways due to competing interactions.

This discovery differs from conventional superconductivity, which involves pairing fermions. Instead, the researchers 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 not only opens up new avenues for the study of quantum materials but also holds potential for developing future technologies that harness these exotic states of matter.