Nonreciprocal magnons in a two-dimensional crystal with out-of-plane magnetization

Abstract

Nonreciprocal spin waves have a chiral asymmetry so that their energy is different for two opposite wave vectors. They are found in atomically thin ferromagnetic overlayers with in-plane magnetization and are linked to the antisymmetric Dzyaloshinskii-Moriya surface exchange. We use an itinerant fermion theory based on first-principles calculations to predict that nonreciprocal magnons can occur in Fe 3 GeTe 2 , the first stand-alone metallic two-dimensional crystal with out-of-plane magnetization. We find that both the energy and lifetime of magnons are nonreciprocal, and we predict that acoustic magnons can have lifetimes up to hundreds of picoseconds, orders of magnitude larger than in other conducting magnets.

Dynamic transverse magnetic susceptibility in the projector augmented-wave method: Application to Fe, Ni, and Co

“…This implies, for example, that magnons can be accessed by perturbing electric fields and that magnons may couple to plasmons and excitons in metals and insulators, respectively. Moreover, spin-orbit coupling may induce topological gaps between magnon branches [52,53], which implies the existence of topological robust surface magnons, or induce nonreciprocity in the magnon dispersion relation [54]. We believe that first principles calculations could help unravel such exotic phenomena in the future.…”

“…In the Supplemental Material [41], we supply a table of threshold values η t corresponding to the intersection with ω = 5 meV found by linear interpolation. As an example, we find η t = 126 meV for iron with the (54,54,54) k-point grid shown in Fig. 5(c) and η t = 87 meV with the (78, 78, 78) k-point grid shown in Fig.…”

“…Magnon peak positions of iron relative to the -peak, in color (left axis), and average displacement frequency, in gray (right axis), as a function of broadening parameter η. Panels (a), (b), (c), and (d) were calculated using (18,18,18), (42,42,42), (54,54,54), and (78, 78, 78) k-point grids, respectively. Red, green, and teal indicate the magnon peaks at wave vectors 1/3 of the way, 2/3 of the way, and at the end of the path → N. The opaque and translucent markers represent results calculated using regular and -centered Monkhorst-Pack grids, respectively.…”

Disentangling Orbital and Valley Hall Effects in Bilayers of Transition Metal Dichalcogenides

“…, where, for the SH conductivity, X η ¼ ŝη and for the OH conductivity (OHC), X η ¼ lη ; ŝη and l η represent the η components of the spin and of the atomic angular momentum operators, respectively. This is implemented in the PAOFLOW code [41] that has been successfully used to study topological materials [42,43] and time dependent spin dynamics [44] among other topics. For our conductivity calculations, we have increased the sampling to 200 × 200 × 1 k points in the 2D BZ.…”

Dynamic transverse magnetic susceptibility in the projector augmented-wave method. Application to Fe, Ni, and Co

“…To study the convergence of the Stoner continuum further, it is worthwhile to remark, that the macroscopic spectrum of Stoner excitations is much cheaper to compute than the full transverse magnetic excitation spectrum, as no extra plane wave components are needed, when the Dyson equation (51) does not have to be inverted. Thus, it would be of great value, if the convergence of the Stoner continuum could be assessed from the Kohn-Sham spectral function itself.…”