Possible Observation of Quadrupole Waves in Spin Nematics

Area of Science:

• Condensed matter physics
• Quantum magnetism
• Materials science

Background:

• Discovery of new states of matter is crucial for technological advancements.
• Quantum spin nematicity is a 'hidden order' state difficult to detect with conventional methods.
• Na_{2}BaNi(PO_{4})_{2} is a candidate material for spin nematicity, suggested by prior observations.

Purpose of the Study:

• To directly confirm the elusive spin nematicity in Na_{2}BaNi(PO_{4})_{2}.
• To investigate the spin excitation spectra in the material's low-temperature phases.
• To elucidate the origin of the low-field spin nematic supersolid phase.

Main Methods:

• Inelastic neutron scattering experiments were performed on Na_{2}BaNi(PO_{4})_{2}.
• Analysis of spin excitation spectra across different magnetic phases.
• Quantitative modeling using a spin-one model.

Main Results:

• Low-energy quadrupole waves, characteristic of spin nematicity, were observed and are absent in conventional magnetic phases.
• A spin-one model accurately reproduced the observed spin excitation spectra, confirming spin nematic orders.
• Evidence for three-magnon continuum and two-magnon bound states was found at the 1/3-magnetization plateau.

Conclusions:

• Direct experimental evidence for quantum spin nematic order in Na_{2}BaNi(PO_{4})_{2} was established.
• The condensation of two-magnon bound states explains the low-field spin nematic supersolid phase.
• This work advances the understanding of hidden order states and their potential applications.