# Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice

## TL;DR

This study introduces Na$_{2}$BaCo(PO$_{4}$)$_{2}$, a new Co-based triangular lattice compound, demonstrating strong quantum fluctuations and no magnetic order down to very low temperatures, making it a promising quantum spin liquid candidate.

## Contribution

The paper reports the discovery and detailed experimental characterization of a new Co-based triangular lattice compound as a quantum spin liquid candidate, with evidence of persistent quantum fluctuations.

## Key findings

- No magnetic ordering down to 0.05 K.
- Presence of localized low-energy spin fluctuations.
- Large magnetic entropy below 1 K.

## Abstract

Currently under active study in condensed matter physics, both theoretically and experimentally, are quantum spin liquid (QSL) states, in which no long-range magnetic ordering appears at low temperatures due to strong quantum fluctuations of the magnetic moments. The existing QSL candidates all have their intrinsic disadvantages, however, and solid evidence for quantum fluctuations is scarce. Here we report a new compound, Na$_{2}$BaCo(PO$_{4}$)$_{2}$, a geometrically frustrated system with effective spin-1/2 local moments for Co$^{2+}$ ions on an isotropic two-dimensional triangular lattice. Magnetic susceptibility and neutron scattering experiments show no magnetic ordering down to 0.05 K. Thermodynamic measurements show that there is a tremendous amount of magnetic entropy present below 1 K in zero applied magnetic field. The presence of localized low-energy spin fluctuations is revealed by inelastic neutron measurements. At low applied fields, these spin excitations are confined to low energy and contribute to the anomalously large specific heat. In larger applied fields, the system reverts to normal behavior as evident by both neutron and thermodynamic results. Our experimental characterization thus reveals that this new material is an excellent candidate for the experimental realization of a quantum spin liquid state.