RIXS observation of bond-directional excitations in the Kitaev material Na2IrO3

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Contributors

  • Marco Magnaterra - , University of Cologne (Author)
  • Karolin Hopfer - , University of Cologne (Author)
  • Christoph J. Sahle - , European Synchrotron Radiation Facility (Author)
  • Marco Moretti Sala - , Polytechnic University of Milan (Author)
  • Giulio Monaco - , University of Padua (Author)
  • Jan Attig - , University of Cologne (Author)
  • Ciarán Hickey - , University of Cologne (Author)
  • Ina Marie Pietsch - , Augsburg University (Author)
  • Franziska Breitner - , Augsburg University (Author)
  • Philipp Gegenwart - , Augsburg University (Author)
  • Mary H. Upton - , Argonne National Laboratory (Author)
  • Jungho Kim - , Argonne National Laboratory (Author)
  • Simon Trebst - , University of Cologne (Author)
  • Paul H.M. van Loosdrecht - , University of Cologne (Author)
  • Jeroen van den Brink - , Clusters of Excellence ctd.qmat: Complexity, Topology and Dynamics in Quantum Matter, Chair of Solid State Theory, Leibniz Institute for Solid State and Materials Research Dresden (Author)
  • Markus Grüninger - , University of Cologne (Author)

Abstract

Spin-orbit coupling locks spin direction and spatial orientation and generates, in semi-classical magnets, a local spin easy-axis and associated ordering. Quantum spin-1/2’s defy this fate: rather than spins becoming locally anisotropic, the spin-spin interactions do. Consequently interactions become dependent on the spatial orientation of bonds between spins, prime theoretical examples of which are Kitaev magnets. Bond-directional interactions imply the existence of bond-directional magnetic modes, spin excitations that render crystallographically equivalent bonds magnetically inequivalent, which yet have remained elusive experimentally. Here we show that resonant inelastic X-ray scattering allows us to explicitly probe the bond-directional character of magnetic excitations. To do so, we use a scattering plane spanned by one bond and the corresponding spin component and scan a range of momentum transfer that encompasses multiple Brillouin zones. Applying this approach to Na2IrO3 we establish the different bond-directional characters of magnetic excitations at ~10 meV and ~45 meV. The bond-directional nearest-neighbor excitations are a fingerprint of the dominant Kitaev interactions and even prevail in the magnetically ordered state.

Details

Original languageEnglish
Article number85
Journalnpj quantum materials
Volume11
Issue number1
Publication statusE-pub ahead of print - 3 Sept 2026
Peer-reviewedYes