[Seminar] Quantum spin entanglement and criticality in 2D triangular magnet KYbSe2

Speaker

Dr. Allen Scheie
Allen Scheie is a postdoctoral research associate in the neutron scattering division of Oak Ridge National Laboratory. He did his PhD under Collin Broholm at Johns Hopkins University, working on experimental studies of frustrated magnetism.

Title

Quantum spin entanglement and criticality in 2D triangular magnet KYbSe₂

Abstract

The Heisenberg triangular lattice quantum spin liquid and the phase transitions to nearby magnetic orders have received much theoretical attention, but clear experimental manifestations of these states are rare. In this talk I will discuss recent experiments on spin-half triangular lattice magnetic delafossite KYbSe₂. Its inelastic neutron spectrum shows reveal a diffuse continuum with a sharp lower bound. Analysis of its magnetic exchange couplings shows it lies very close to the theoretical J₂/J₁ Heisenberg quantum spin liquid phase. Applying entanglement witnesses to the data reveals multipartite entanglement spread between its neighbors, and comparing the experimental diffuse scattering data with Schwinger Boson and tensor network simulations strongly suggests the presence of bound spinon quasiparticles. We also find evidence of quantum critical scaling in the dynamical structure factor, indicating a second order transition to the spin liquid phase. Comparing this to previous theoretical work suggests that the proximate phase is a gapped ℤ₂ spin liquid, resolving a long-debated issue. These various experimental and theoretical tools show remarkable consistency, and all point to strong quantum effects from a proximate spin liquid phase. This not only reveals details about the theoretical phase diagram itself, but also indicates a route for experimentally identifying a true quantum spin liquid state.

Reference:  [1] Scheie et al, ArXiv:2109.11527

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