Quantum entanglement of XY-type spin dimers in Shastry-Sutherland lattice

TL;DR

This study reveals that BaCe$_2$ZnS$_5$ exhibits a quantum paramagnet state with entangled XY-type spin dimers, lacking magnetic order down to very low temperatures, confirmed by neutron scattering and thermodynamic measurements.

Contribution

It introduces a localized spin dimer model with XY anisotropy that accurately explains the disordered ground state of BaCe$_2$ZnS$_5$, highlighting the role of entangled dimers.

Findings

Lack of magnetic order down to 73 mK.

Ground state is an entangled spin dimer state.

Strong XY-type anisotropy in intra-dimer exchange.

Abstract

We report a comprehensive study on the origin of the enigmatic disordered ground state within the Shastry-Sutherland lattice, BaCe$_2$ZnS$_5$, at low temperatures. The magnetization and heat capacity data show a lack of magnetic ordering down to 73 mK. We deploy a localized spin dimer model which can accurately reproduce the dynamic structure factor of the neutron data, magnetization and heat capacity data. Remarkably, the intra-dimer exchange interaction shows strong XY-type anisotropy and the ground state of BaCe$_2$ZnS$_5$ is in an entangled state $(|\uparrow\uparrow> - |\downarrow\downarrow>)/\sqrt{2}$. This is in contrast to the singlet dimer state that is obtained for Heisenberg interactions. These results confirm that BaCe$_2$ZnS$_5$ is in a quantum paramagnet state consisting of entangled spin dimer states.