Orbital Nernst Effect of Magnons

Abstract

In the past, magnons have been shown to mediate thermal transport of spin in various systems. Here, we reveal that the fundamental coupling of scalar spin chirality, inherent to magnons, to the electronic degrees of freedom in the system can result in the generation of sizeable orbital magnetization and thermal transport of orbital angular momentum. We demonstrate the emergence of the latter phenomenon of orbital Nernst effect by referring to the spin-wave Hamiltonian of kagome ferromagnets, predicting that in a wide range of systems the transverse current of orbital angular momentum carried by magnons in response to an applied temperature gradient can overshadow the accompanying spin current. We suggest that the discovered effect fundamentally correlates with the topological Hall effect of fluctuating magnets, and it can be utilized in magnonic devices for generating magnonic orbital torques.

Topological–chiral magnetic interactions driven by emergent orbital magnetism

“…Here, based on microscopic arguments and a systematic total-energy expansion, we discover a conceptually new class of chiral interactions between spins on triangular plaquettes, which originates from the TOM of electrons. We refer to these interactions as topological-chiral interactions, favouring the emergence of non-coplanar magnetic structures with scalar spin chirality of specific sign even without an external magnetic field, either in the ground state or as a result of thermal fluctuations 29 . The first type of topological-chiral interactions is the rotation-invariant chiral-chiral interaction (CCI), which in its general form corresponds to the interaction between pairs of topological orbital currents in a magnet, just in analogy to Ampère's observation that the force between wires can be described by the effective interaction of currents.…”

Magnon hybridization in ferrimagnetic heterostructures

“…They can be activated by microwave [3,4], laser [5][6][7] and thermal fluctuation [8][9][10] and interact with each other through, e.g., exchange coupling [11,12] and magnetic dipolar interaction [11,13,14]. In the past decade, many interesting magnon-related phenomena, such as spin Seebeck effect (SSE) [8,15], orbital Nernst effect of magnon [16] and corner states in ferromagnetic breathing Kagome lattice [17], have been reported. To understand the underlying physics of these phenomena, we need to explore the properties of magnons.…”