Gapless Dirac magnons in CrCl${}_3$

Abstract

Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX${}_3$ (X=Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr${}_3$ and CrI${}_3$, gapless Dirac magnons are present in bulk CrCl${}_3$, with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac $K$ point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above T${}_N$. Moreover, an unusual negative thermal expansion (NTE) of the $a$-axis lattice constant and anomalous phonon behavior are observed below 50 K, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above T${}_N$.

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References in corpus (6)

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• Topological Magnons: A Review
• Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr${}_3$
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Cited by in corpus (9)

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• Self-selecting vapor growth of transition metal halide single crystals
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• Investigating the magneto-elastic properties in FeSn and Fe${}_3$Sn${}_2$ flat band metals
• Linear response theories for interatomic exchange interactions
• Antiferromagnetic-ferromagnetic homostructures with Dirac magnons in van der Waals magnet CrI${}_3$
• Magnon dispersion and spin transport in CrCl${}_3$ bilayers under different strain-induced magnetic states
• Probing GHz Spin Dynamics Across Magnetic Phase Transitions in CrCl3 Nanoflakes Using Nitrogen-Vacancy Microscopy
• Transport of Dirac magnons driven by gauge fields