Quasi-two-dimensional frustrated spin-1 triangular lattice antiferromagnet Ca3NiNb2O9: A proximate spin liquid

The spin-1 triangular lattice Heisenberg antiferromagnet $\mathrm{C}{\mathrm{a}}_3\mathrm{NiN}{\mathrm{b}}_2{\mathrm{O}}_9$ and its sister compounds are conjectured to promote the formation of many-body quantum entangled states such as a quantum spin liquid (QSL), an exotic phase which features fractionalized quasiparticle excitations and emergent gauges. We probe the single crystal of $\mathrm{C}{\mathrm{a}}_3\mathrm{NiN}{\mathrm{b}}_2{\mathrm{O}}_9$ using an in-depth Raman spectroscopic technique. Our measurements provide evidence for the fractionalized excitations, suggesting that the current system is in close proximity to the QSL phase. This is also in line with the proposed higher-order fractional magnetization plateau in this system, as these plateaus have an intricate relationship with the spin entanglement. We observed unconventional underlying scattering as a broad continuum with an intensity that shows fermionic statistics. Additionally, phonon modes show Fano asymmetry, also conjectured as a fingerprint of the spin-liquid phase, and above a critical Raman shift also show fermionic statistics in their intensity evolution.