Unconventional bipartite entanglement in the quantum dimer magnet Yb₂Be₂SiO₇

The quantum dimer magnet, with antiferromagnetic intradimer and interdimer Heisenberg exchange between spin-1/2 moments, is known to host an $\left(\left(\uparrow \downarrow \right)-\left(\downarrow \uparrow \right)\right)/\sqrt{2}$ singlet ground state when the intradimer exchange is dominant. Rare-earth-based quantum dimer systems with strong spin-orbit coupling offer the opportunity for tuning their magnetic properties by using magnetic anisotropy as a control knob. Here, we present bulk characterization and neutron scattering measurements of the quantum dimer magnet Yb₂Be₂SiO₇. We find that the Yb³⁺ ions can be described by an effective spin-1/2 model at low temperatures and the system does not show signs of magnetic order down to 50 mK. The magnetization, heat capacity, and neutron spectroscopy data can be well-described by an isolated dimer model with highly anisotropic exchange that stabilizes a singlet ground state with a wavefunction $\left(\left(\uparrow \uparrow \right)-\left(\downarrow \downarrow \right)\right)/\sqrt{2}$ or $\left(\left(\uparrow \uparrow \right)+\left(\downarrow \downarrow \right)\right)/\sqrt{2}$ . Our results show that strong spin-orbit coupling can induce unusual entangled states of matter in quantum dimer magnets.