Abstract
The latest experimental advances have extended the scenario of coupling mechanical degrees of freedom in chiral magnets (MnSi/MnGe) to the topologically nontrivial skyrmion crystal and even monopole lattices. Equipped with a spin-wave theory highlighting the topological features, we devise an interacting model for acoustic phonons and magnons to explain the experimental findings in a monopole lattice with a topological phase transition, i.e. annihilation of monopole–antimonopole pairs. We reproduce the anisotropic magnetoelastic modulations of elastic moduli: drastic ultrasonic softening around the phase transition and a multi-peak-and-trench fine structure for sound waves parallel and orthogonal to the magnetic field, respectively. Comparison with experiments indicates that the magnetoelastic coupling induced by Dzyaloshinskii–Moriya interaction is comparable to that induced by the exchange interaction. Other possibilities such as elastic hardening are also predicted. The study implies that the monopole defects and their motion in MnGe play a crucial role.
Highlights
Topology is playing a more and more significant role in condensed matter physics.Apart from an upsurge in the focus on topological classification of quantum phases of matter, another field bearing ideas of topology, magnetism inhabited by stripes, vortices, domain walls, etc., has been under experimental and theoretical investigations for a long history[1]
This work aims at highlighting the effect characteristic for the topologically nontrivial defects and the orientational field n(r), which is inherently described by the second homotopy group of a 2-sphere S2 that cannot shrink to a point, naturally appears to be physically more relevant
The electromagnetic fields (EEMF) helps describe itinerant electrons coupled with localized spins and captures the essential feature of the nontrivial spin texture, we find it rather informative even for the magnetoelastic response to be discussed
Summary
Topology is playing a more and more significant role in condensed matter physics. Apart from an upsurge in the focus on topological classification of quantum phases of matter, another field bearing ideas of topology, magnetism inhabited by stripes, vortices, domain walls, etc., has been under experimental and theoretical investigations for a long history[1]. Symmetry breaking of spins in noncentrosymmetric chiral magnets, which bears both the Heisenberg exchange interaction (EXI) and the Dzyaloshinskii-Moriya interaction (DMI)[30, 31, 32] due to spin-orbit coupling, can embody the Skyrmion texture[2, 3]. A minimal Hamiltonian for isolated Skyrmions or a Skyrmion lattice in d spatial dimensions includes the EXI, the Bloch-type DMI, and the Zeeman energy[33, 34]. Revives the old idea originally proposed as a hadron model[12], serving as a new scenario of the interplay between the orbital and spin of electrons and ions, and offering plenty of brand new phenomena[13, 14, 15, 16, 17, 18, 19, 20, 21, 22] together with the potential for application in magnetic storage[23, 24, 25, 26, 27, 28, 29].
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