Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe${}_3$

Abstract

Spin and lattice are two fundamental degrees of freedom in a solid, and their fluctuations about the equilibrium values in a magnetic ordered crystalline lattice form quasiparticles termed magnons (spin waves) and phonons (lattice waves), respectively. In most materials with strong spin-lattice coupling (SLC), the interaction of spin and lattice induces energy gaps in the spin wave dispersion at the nominal intersections of magnon and phonon modes. Here we use neutron scattering to show that in the two-dimensional (2D) van der Waals honeycomb lattice ferromagnetic CrGeTe3, spin waves propagating within the 2D plane exhibit an anomalous dispersion, damping, and break-down of quasiparticle conservation, while magnons along the c axis behave as expected for a local moment ferromagnet. These results indicate the presence of dynamical SLC arising from the zero-temperature quantum fluctuations in CrGeTe3, suggesting that the observed in-plane spin waves are mixed spin and lattice quasiparticles fundamentally different from pure magnons and phonons.

12 pages, 4 figures; Nature Communication in press

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• Visualizing thickness-dependent magnetic textures in few-layer ${\text{Cr}}_2{\text{Ge}}_2{\text{Te}}_6$
• Magnon spectrum of altermagnets beyond linear spin wave theory: Magnon-magnon interactions via time-dependent matrix product states vs. atomistic spin dynamics
• Sizable suppression of magnon Hall effect by magnon damping in Cr${}_2$Ge${}_2$Te${}_6$
• Exchange striction induced thermal Hall effect in van der Waals antiferromagnet MnPS${}_3$
• Two-Step Electronic Response to Magnetic Ordering in a van der Waals Ferromagnet
• Spontaneously formed phonon frequency combs in van der Waals solid CrXTe${}_3$ (X=Ge,Si)
• Tuning magnetic exchange interactions in 2D magnets: the case of CrGeX${}_3$ (X = Se, Te) and Janus Cr${}_2$Ge${}_2$(Se,Te)${}_3$ monolayers
• Pressure tuning of intrinsic and extrinsic sources to the anomalous Hall effect in CrGeTe${}_3$
• Nonlocal damping of spin waves in a magnetic insulator induced by normal, heavy, or altermagnetic metallic overlayer: A Schwinger-Keldysh field theory approach
• Correlation stabilized ferromagnetic MnRuAs with distorted kagome lattice
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