Title: The Ghost of Vanished Stripe Order in Triangular Lattice Quantum Magnets

Speaker: Wei Li, School of Physics, Beihang University

Time: 9:30 am, Wednesday, Mar. 11, 2020 (UTC/GMT+08:00)

Online venue: Zoom online meeting ID: 459 673 910

Abstract: In this talk, I would like to present our recent work on triangular-lattice quantum magnets, where spin frustration gives rise to rather unexpected excitations and thus finite-temperature behaviors. With newly developed thermal tensor network method, we are able to determine the magnetic “genome” of quantum materials. In the compound Ba8CoNb6O24 (BCNO), we find a virtually ideal realization of triangular-lattice Heisenberg model, and in the material TmMgGaO4 (TMGO) a triangular-lattice transverse-field Ising model. In these two intriguing magnetic materials, soft modes exist at M point of Brillouin zone, as ghost of a vanished competing stripe order, which significantly influence the intermediate-temperature thermodynamics. Through accurate quantum many body computations, we reveal in BCNO an unexpected two-temperature-scale scenario, and in TMGO a long-sought Kosterlitz-Thouless phase of 2D magnets. In the latter, we further interpret the stripy “ghost” as vortex-antivortex pair excitation.