Spin supersolidity in nearly ideal easy-axis triangular quantum antiferromagnet Na2BaCo(PO4)2

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 Na2BaCo(PO4)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 analog 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.

From RVB to supersolidity: the saga of the Ising-Heisenberg model on the triangular lattice

“…At much lower temperature, another peak has been detected [12]. Its rounded shape suggests that it could be the trace of the BKT transition into the "Y" shaped supersolid predicted by Gao et al [9]. This is supported by the observation that this line seems to terminate at a quantum critical point at 0.8 T (see Fig.…”

“…This is another spin-supersolid phase. Both spin-supersolid phases have been predicted to be separated from the plateau phase by a Berezinskii-Kosterlitz-Thouless (BKT) transition [9]. The development of three-sublattice long-range order coming from high temperature is expected to remain 3-state Potts, except at high field where a single transition into the "V" phase has been predicted.…”

Dipolar Spin Liquid Ending with Quantum Critical Point in a Gd-based Triangular Magnet

“…The intriguing spin frustration effects and two dimensionality of such systems imply Berezinskii-Kosterlitz-Thouless (BKT) physics may appear at low temperatures. Indeed, the Co-based quantum antiferromagnet Na 2 BaCo(PO 4 ) 2 hosts persistent spin fluctuations [17][18][19][20] till very low temperature, and is proposed to realize spin supersolidity with prominent BKT phase fluctuations [21]. Besides, emergent symmetry has also been disclosed on the triangular lattice as a consequence of strong frustration, with a primary example of rare-earth magnet TmMgGaO 4 [22][23][24][25][26][27].…”