Electromagnetic effects induced by a time-dependent axion field

Abstract

We studied the dynamics of the so-called θ-term, which exists in topological materials and is related to a hypothetical field predicted by Peccei-Quinn in particle physics, in a magnetic superlattice constructed using a topological insulator and two ferromagnetic insulators, where the ferromagnetic insulators had perpendicular magnetic anisotropies and different magnetic coercive fields. We examined a way to drive the dynamics of the θ-term in the magnetic superlattice through changing the inversion symmetry (from an anti-parallel to a parallel magnetic configuration) using an external magnetic field. As a result, we found that unconventional electromagnetic fields, which are magnetic field-induced charge currents and vice versa, are generated by the nonzero dynamics of the θ-term.

Topological Axion States in the Magnetic Insulator MnBi2Te4 with the Quantized Magnetoelectric Effect

“…The magnetic fluctuation of the Néel order leads to linear contribution to the fluctuation of axion field, and the static θ deviates from π. While in the case of AFM1 MnBi 2 Te 4 , the Néel order conserves both I and S, thus the static θ = π, and to the linear order, the magnetic fluctuation has no contribution to the dynamics of axion field [40,58].…”

Conserved laws and dynamical structure of axions coupled to photons

“…It is important to note that the term (κ/8π 2 )∂ µ θA ν F µν present in the action (2), which contributes the third and sixth term to (24), renders the improved non-symmetric energy-momentum tensor, which indicates Lorentz violation. Nevertheless, T µν imp satisfies the correct conservation law in the sense that its on-shell divergence vanishes, ∂ µ T µν imp = 0.…”

“…In this scenario, the total derivative can be omitted as it does not contribute to the classical field equations, which does not alter the dynamical content of modified axion electrodynamics. Physically, the electromagnetic interaction of the dynamical axion significantly affects the behavior of electromagnetic propagating modes, as happens with magnetically doped topological insulators having continuous values of θ, dubbed as topological magnetic insulators [11,23,24]. Interesting effects due to the dynamical axion field have been predicted in the presence of an applied magnetic field, such as the dynamical chiral magnetic effect, where an alternating electric current is generated by static magnetic fields from dynamical axion field induced by an antiferromagnetic resonance, which is absent in standard topological insulator.…”

Axion-matter coupling in multiferroics

“…Traditionally, the majority of axion detection proposals have focused on exploiting the axion-photon coupling in cavities or plasma haloscopes using strong external fields [11][12][13][14][15][16][17][18][19][20][21] . More recently, axion physics has been increasingly discussed in the quantum condensed matter context [22][23][24][25] primarily in analogy to axion electrodynamics in topological insulators [26][27][28][29][30] , but also in terms of particle axion detection via resonant coupling to quasiparticles 31 . In most of the existing proposals, the detection scheme uses DM particle absorption to induce single particle excitations in the sensor material, e.g.…”