Magnetic resonance induced pseudoelectric field and giant current response in axion insulators

Abstract

A quantized version of the magnetoelectric effect, known as the topological magnetoelectric effect, can exist in a time-reversal invariant topological insulator with all its surface states gapped out by magnetism. This topological phase, called the axion insulator phase, has been theoretically proposed but is still lack of conclusive experimental evidence due to the small signal of topological magnetoelectric effect. In this work, we propose that the dynamical in-plane magnetization in an axion insulator can generate a "pseudo-electric field", which acts on the surface state of topological insulator films and leads to the non-zero response current. Strikingly, we find that the current at magnetic resonance (either ferromagnetic or anti-ferromagnetic) is larger than that of topological magnetoelectric effect by several orders of magnitude, and thereby serves as a feasible smoking gun to confirm the axion insulator phase in the candidate materials.

Recent Progress in Proximity Coupling of Magnetism to Topological Insulators

“…Researchers have predicted that the single SL of MnBi 2 Te 4 is a trivial 2D FMI and the topological and magnetic nature of this material can be tuned by varying the thickness, [ 78 ] with axion insulator occurring in even number of SLs and QAHI in odd number (greater than 1) of SLs. [ 78,79,85,86 ] The reason that the QAHE can survive in odd‐numbered SLs of MnBi 2 Te 4 is that the magnetic moments of all SLs but one compensate each other, yielding an uncompensated anti‐ferromagnetic state. [ 87 ] This material has been successfully synthesized by both molecular beam epitaxy (MBE) [ 88 ] and single crystal growth.…”

Pseudo-gauge Fields in Dirac and Weyl Materials

“…Ref. [39] suggests that the desired pseudo-electric field can be induced by the dynamical magnetization of the FMIs, as discussed below.…”

“…In MnBi 2 Te 4 , Ref. [39] suggests the pseudo-gauge field can be given by anti-ferromagnetic resonance and further induces nonzero current response, through a similar mechanism. Besides the pseudo-gauge field mechanism, dynamical magnetization can also make the axion field dynamical and then induce a nonzero response of axion insulators [43,44].…”

“…When tuning the frequency to induce the ferromagnetic resonance, Ref. [39] shows that the magnetization-induced J M can be much larger than J B . Specifically, with typical values of parameters, the ratio between the maximum values of J M and J B is about 20 ∼ 2 × 10 4 depending on the material for FMIs.…”

Dynamical Piezomagnetic Effect in Time-Reversal-Invariant Weyl Semimetals with Axionic Charge-Density Waves

“…A direct physical consequence of nonzero θ bulk is the magnetoelectric effect 22 , where an external electric (magnetic) field induces a magnetization (polarization) in the parallel direction; if quantized by an axionodd symmetry, the effect is called the topological magnetoelectric effect 22,37,38 . Other physical consequences of a non-zero θ bulk include the surface half QAHE 22 , a giant magnetic-resonance-induced current [39][40][41] , the topological magneto-optical effect [42][43][44] (especially its exact quantization 42 ), the zero-Hall plateau state [45][46][47] , and the image magnetic monopole 48 .…”