Researchers achieve Bose-Einstein condensation of bound magnon pairs in triangular lattice material

Researchers achieve Bose-Einstein condensation of bound magnon pairs in triangular lattice material
by Simon Mansfield
Sydney, Australia (SPX) Mar 17, 2025

Using advanced magnetic field instrumentation, scientists have for the first time experimentally observed Bose-Einstein condensation (BEC) of bound magnon pairs in a spin-1 triangular lattice. This milestone was achieved through collaborative efforts by researchers from Southern University of Science and Technology, Zhejiang University, Renmin University of China, and the Australian Nuclear Science and Technology Organization, employing the Multi-frequency High Field Electron Spin Resonance Spectrometer at the Steady-State High Magnetic Field Facility (SHMFF) housed within the Hefei Institutes of Physical Science, Chinese Academy of Sciences.

The breakthrough, recently reported in *Nature Materials*, demonstrates a long-theorized but previously unverified quantum phenomenon in magnetic systems. BEC, a state where particles known as bosons coalesce into a unified quantum state at extremely low temperatures, has been observed in cold atomic gases, but this marks the first time it has been identified in a bound state of magnons-the fundamental quanta of spin waves-within a magnetic material.

The team studied Na2BaNi(PO4)2, a magnetic compound characterized by its triangular lattice structure, which induces what physicists call "frustrated magnetism." In such a system, competing interactions between electron spins prevent them from aligning in a simple pattern, giving rise to complex quantum behavior. This structure provided a fertile ground to investigate how two magnons can pair up, forming a composite entity that condenses collectively into a BEC.

Unlike traditional superconductivity, where paired fermions (such as electrons) form a coherent quantum state, this discovery centers on bosonic magnon pairs undergoing condensation. "Our results reveal a novel type of quantum phase transition driven by magnon pairing, shedding light on previously unexplored states of quantum matter," the researchers noted.

SHMFF's high sensitivity enabled the detection of subtle spectral signatures indicative of two-magnon bound states. The experimental data aligned closely with theoretical models, and corroborating studies using low-temperature thermodynamics, neutron scattering, and nuclear magnetic resonance techniques provided additional evidence supporting the existence of this unique BEC state.

According to the research team, this discovery not only validates theoretical predictions but also opens new pathways for studying exotic phases in quantum materials, with potential applications in future quantum technologies.

Research Report:Bose-Einstein condensation of a two-magnon bound state in a spin-1 triangular lattice