부산대학교 도서관

The Heisenberg triangular lattice quantum spin liquid and the phasetransitions to nearby magnetic orders have received much theoretical attention,but clear experimental manifestations of these states are rare. This workinvestigates a new spin-half Yb$^{3+}$ delafossite material, KYbSe$_2$, whoseinelastic neutron scattering spectra reveal a diffuse continuum with a sharplower bound. Applying entanglement witnesses to the data reveals significantmultipartite entanglement spread between its neighbors, and analysis of itsmagnetic exchange couplings shows close proximity to the triangular latticeHeisenberg quantum spin liquid. Key features of the data are reproduced bySchwinger-boson theory and tensor network calculations with a significantsecond-neighbor coupling $J_2$. The strength of the dynamical structure factorat the $K$ point shows a scaling collapse in $\hbar\omega/k_\mathrm{B}T$ downto 0.3 K, indicating a second-order quantum phase transition. Comparing this toprevious theoretical work suggests that the proximate phase at larger $J_2$ isa gapped $\mathbb{Z}_2$ spin liquid, resolving a long-debated issue. We thusshow that KYbSe$_2$ is close to a spin liquid phase, which in turn sheds lighton the theoretical phase diagram itself.