Topological properties of microwave magnetoelectric fields

Abstract

Collective excitations of electron spins in a ferromagnetic sample dominated by the magnetic dipole-dipole interaction strongly influence the field structure of microwave radiation. A small quasi-two-dimensional ferrite disk with magnetic-dipolar-mode (MDM) oscillation spectra can behave as a source of specific fields in vacuum, termed magnetoelectric (ME) fields. A coupling between the time-varying electric and magnetic fields in the ME-field structures is different from such a coupling in regular electromagnetic fields. The ME fields are characterized by strong energy confinement at a subwavelength region of microwave radiation, topologically distinctive power-flow vortices, and helicity parameters [E. O. Kamenetskii, R. Joffe, and R. Shavit, Phys. Rev. E 87, 023201 (2013)]. We study topological properties of microwave ME fields by loading a MDM ferrite particle with different dielectric samples. We establish a close connection between the permittivity parameters of dielectric environment and the topology of ME fields. We show that the topology of ME fields is strongly correlated with the Fano-resonance spectra observed at terminals of a microwave structure. We reveal specific thresholds in the Fano-resonance spectra appearing at certain permittivity parameters of dielectric samples. We show that ME fields originated from MDM ferrite disks can be distinguished by topological portraits of the helicity parameters and can have a torsion degree of freedom. Importantly, the ME-field phenomena can be viewed as implementations of space-time coordinate transformations on waves.

Unidirectional magnetoelectric-field multiresonant tunneling

“…These specific near fields -the ME fields -give evidence for spontaneous symmetry breakings at the resonant states of MDM oscillations. This symmetry breaking is characterized by the helicity parameter [13,15,52]. The ME-field singularity is strongly related to edge chiral currents.…”

“…In our previous studies [13,15,40,52], it was shown that topology of the near fields originated from a MDM ferrite disk -the ME fields -is characterized both by the power-flow vortices and the helicity parameters. While the power transmission in a two-port microwave structure is strongly related to the power-flow vortices of the twisting excitations, the helicity characteristics of these excitations (being local characteristics of the field geometry) are very slightly correlated with the power transmission effect.…”

Quantization of magnetoelectric fields

“…In a structure of a thin rectangular waveguide with an embedded quasi-2D ferrite disk [36], the contact regions can be considered as two vacuum cylinders with the same diameter as a ferrite disk. This model is inapplicable in a case of a "thick" microwave waveguide [82,83]. However, use of two dielectric cylinders with a high dielectric constant allows considering these cylinders as the contact regions in a "thick" microwave waveguide.…”

Chiral-field microwave antennas Chiral microwave near fields for far-field radiation

“…Because of rotations of localized field configurations in a fixed observer inertial frame, the linking between the EM and ME fields cause violation of the Lorentz symmetry of spacetime. In such a sense, ME fields can be considered as Lorentz-violating extension of the Maxwell equations [5,6].…”

“…To characterize the ME-field singularities, the helicity (chirality) parameter was introduced. A time average helicity parameter for the near fields of a ferrite disk with MDM oscillations is defined as [5,6,14]:…”