Spin Supersolidity in Nearly Ideal Easy-axis Triangular Quantum Antiferromagnet Na$_2$BaCo(PO$_4$)$_2$

TL;DR

This paper demonstrates that Na$_2$BaCo(PO$_4$)$_2$ is an almost ideal realization of a spin-1/2 triangular antiferromagnet with easy-axis anisotropy, hosting a spin supersolid state that breaks both lattice and spin symmetries.

Contribution

The study provides a microscopic model for NBCP that fits experimental data and predicts a spin supersolid phase, advancing understanding of quantum magnetism and supersolidity in real materials.

Findings

NBCP hosts a spin supersolid state.

The model accurately reproduces thermodynamic and magnetization data.

NBCP is an ideal platform for exploring supersolidity.

Abstract

Prototypical models and their material incarnations are cornerstones to the understanding of quantum magnetism. Here we show theoretically that the recently synthesized magnetic compound Na$_2$BaCo(PO$_4$)$_2$ (NBCP) is a rare, nearly ideal material realization of the $S=1/2$ triangular-lattice antiferromagnet with significant easy-axis spin exchange anisotropy. By combining the automatic parameter searching and tensor-network simulations, we establish a microscopic model description of this material with realistic model parameters, which can not only fit well the experimental thermodynamic data but also reproduce the measured magnetization curves without further adjustment of parameters. According to the established model, the NBCP hosts a spin supersolid state that breaks both the lattice translation symmetry and the spin rotational symmetry. Such a state is a spin analogue of the long-sought supersolid state, thought to exist in solid Helium and optical lattice systems, and share similar traits. The NBCP therefore represents an ideal material-based platform to explore the physics of supersolidity as well as its quantum and thermal melting.