Speaker: Sara Haravifard (Duke University)

Host: Chandan Setty

Title: From Dirac Spin Liquids to Hidden Multipolar Order: Quantum Magnetism in YbZn2GaO5 and TmZn2GaO5

Abstract: Rare-earth triangular lattice magnets continue to provide fertile ground for discovering unconventional quantum states arising from strong frustration, anisotropy, and the interplay of exchange interactions with crystal electric field physics. In this talk I will present our recent work on two structurally related triangular-lattice rare-earth magnets that host strikingly different quantum ground states. I begin with YbZn2GaO5, a spin-1/2 system where low-temperature T2 specific heat, momentum-selective excitation continua, and a gap at the Γ point collectively identify a U(1) Dirac quantum spin liquid with spinon excitations centered at the K and M points. This establishes YbZn2GaO5 as a crystalline realization of a Dirac QSL. I then turn to TmZn2GaO5, an Ising-anisotropic non-Kramers magnet with a pseudo-doublet ground state. Despite strong antiferromagnetic interactions, the material shows no long-range order down to 50 mK. Neutron scattering reveals a gapped mode at the K point, and theory places the system in the quantum-disordered multipolar phase of the transverse-field Ising model—featuring a hidden multipolar polarization invisible to elastic neutron probes. Together, these materials showcase how small changes in rare-earth electronic structure produce fundamentally different emergent quantum states—ranging from fractionalized spin liquids to nonmagnetic multipolar phases—within the same triangular-lattice architecture.