Block magnetic excitations in the orbitally-selective Mott insulator BaFe$_2$Se$_3$

ORAL

Abstract

We investigate the spectrum of magnetic excitations in the Fe-based two-leg ladder material BaFe$_2$Se$_3$ by means of broad-band inelastic neutron scattering. BaFe$_2$Se$_3$ garnered recent attention due to its quasi-1D structure and as hosting an exotic block magnetic ground-state where 4 Fe spins co-align to form Fe$_4$ plaquettes. Our neutron results provide a detailed understanding of magnetic excitations originating from the Fe$_4$ block ground-state. Consisting of a 50 meV wide band of quasi-1D acoustic spin-waves and three high-energy modes around 100 meV and 200 meV, the spin fluctuations and the static moment carry a total squared magnetic moment of 16 $\mu_{\rm B}^2$ per Fe, indicative of orbital selectiveness for localized spins. We develop an effective Heisenberg model that accounts for the observed spectrum and provides a set of exchange interactions to understand how exotic magnetism stems from strong lattice, orbital and electronic correlations in iron chalcogenides.

*Work at IQM supported by the U.S. D.O.E, Office of Basic Energy Sciences, Division of Material Sciences and Engineering under grant DE-FG02-08ER46544. Research at ORNL's SNS supported by U.S. D.O.E, Office of B.E.S., Scientific User Facilities Division

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Authors

  • M. Mourigal

    • Johns Hopkins University and Georgia Institute of Technology

  • Shan Wu

    • Johns Hopkins University

  • M.B. Stone

    • Oak Ridge National Laboratory

  • J.R. Neilson

    • Johns Hopkins University and Colorado State University

  • J.M. Caron

    • Johns Hopkins University and Cornell University

  • T.M. McQueen

    • Johns Hopkins University

  • C.L. Broholm

    • Johns Hopkins University and Oak Ridge National Laboratory