Chiral coupling of magnons in waveguides

Abstract

We theoretically investigate the collective excitation of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnonphoton coupling can be tuned to be chiral, i.e., magnons only couple with photons propagating in one direction, leading to asymmetric transfer of angular momentum and energy between the magnets. A large imbalance in the magnon number distribution over the magnets can be achieved with a long chain of magnets, which concentrate at one edge. The chain also supports standing waves with low radiation efficiency that is inert to the chirality. arXiv:1909.01817v1 [cond-mat.mes-hall]

Circulating cavity magnon polaritons

“…Analogous with structures that are coupled by optical resonators [17], metamaterials [18], and dielectric nanostructures [19,20], multiple magnets inside a cavity form new collective modes by the real or virtual exchange of cavity photons [10,21,22]. The polarization-momentum coupling of confined electromagnetic waves [23][24][25] can be employed to realize magnet-based broadband nonreciprocity and devices such as circulators [26,27] and a magnon accumulation in an open waveguide [28][29][30].…”

“…According to Maxwell's equation, the polarization of some cavity modes is "locked" to their propagation direction at special planes or lines in cavities or wave guides. Chiral coupling is then achieved when magnets positioned on these planes resonate with the photon mode frequency [28][29][30].…”

Giant Microwave Sensitivity of Magnetic Array by Long-Range Chiral Interaction Driven Skin Effect

“…Chirality is a common ingredient in topological magnetic orders [10][11][12], but in terms of which realization of non-Hermitian topology is rarely addressed [13,14]. Chiral interaction between Kittel magnon of a magnetic wire (or sphere) has been recently discovered when they couple with the traveling modes such as the spin waves in films [15][16][17][18], waveguide microwaves [19,20], and surface acoustic waves [21][22][23], to name a few, in that the Kittel modes prefer to couple with the traveling waves propagating in one direction. We have argued that these traveling waves can mediate a long-range chiral interaction between two magnetic wires if their damping is not large [17,18].…”

“…It could be thereby speculated that these long-range chiral interaction might lead to a similar non-Hermitian skin effect to that by the chiral short-range interaction in Hatano-Nelson model [2] since the energy tends to accumulate at one end. However, theoretical effort showed that these systems do not favor the coalesce of bulk modes [19] but only hold weak skin tendency for those modes with large decay rates, nor were the edge modes ever observed by experiments [18,[24][25][26]. The strong interference brought by the propagation of the traveling waves may be detrimental for the accumulation.…”

Noncontact Spin Pumping by Microwave Evanescent Fields

“…In this Letter, we address the noncontact angular momentum transfer to an electric conductor by stray magnetic fields emitted by an excited magnet, thereby generalizing the concept of spin pumping by a contact exchange interaction [18,19]. We are motivated by the significant near fields that couple magnetic nanowires and ultrathin magnetic insulating films, causing several chiral magnon transport phenomena [17,[20][21][22][23][24][25][26].…”