Symmetry conditions for nonreciprocal light propagation in magnetic crystals

Szaller, D.; Bordács, S.; Kézsmárki, I.

doi:10.1103/physrevb.87.014421

Cited by 84 publications

(71 citation statements)

References 61 publications

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“…The interference term, that is, /0|m j |nS/n|p i |0S matrix element product, is sensitive to the relative orientation of the static electric polarization and the static magnetization in multiferroics. Indeed directional dichroism can emerge in multiferroics where the ferroelectric polarization is not parallel to the magnetization 7,12,14,15 , in magnets with ferrotoroidic order 7 , and in the present case of magnetically induced chirality. Therefore, the measurement of directional anisotropy may be applied for spatial mapping of multiferroic domain structures, a capability that has been considered to be the privilege of non-linear optical techniques such as the optical second harmonic generation [51][52][53][54] .…”

Section: Magnetoelectric Effect Governed By Directional Dichroismmentioning

confidence: 99%

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One-way transparency of four-coloured spin-wave excitations in multiferroic materials

et al. 2014

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The coupling between spins and electric dipoles governs magnetoelectric phenomena in multiferroics. The dynamical magnetoelectric effect, which is an inherent attribute of the spin excitations in multiferroics, drastically changes the optical properties of these compounds compared with conventional materials where light-matter interaction is expressed only by the dielectric permittivity or magnetic permeability. Here we show via polarized terahertz spectroscopy studies on multiferroic Ca 2 CoSi 2 O 7 , Sr 2 CoSi 2 O 7 and Ba 2 CoGe 2 O 7 that such magnetoeletric spin excitations exhibit quadrochroism, that is, they have different colours for all the four combinations of the two propagation directions (forward or backward) and the two orthogonal polarizations of a light beam. We demonstrate that one-way transparency can be realized for spin-wave excitations with sufficiently strong optical magnetoelectric effect. Furthermore, the transparent and absorbing directions of light propagation can be reversed by external magnetic fields. This magnetically controlled optical-diode function of magnetoelectric multiferroics may open a new horizon in photonics.

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Section: Magnetoelectric Effect Governed By Directional Dichroismmentioning

confidence: 99%

“…In materials with simultaneously broken spatial inversion and time reversal symmetry this two-fold ± k directional degeneracy of the Maxwell equations can be lifted and each of the four waves may be absorbed with a different strength [3][4][5][6][7] . We call this phenomenon quadrochroism and the corresponding materials quadrochroic or four-coloured media.…”

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confidence: 99%

One-way transparency of four-coloured spin-wave excitations in multiferroic materials

et al. 2014

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“…Spectroscopic investigations have since been performed from the microwave 11,[32][33][34] to the visible 31 frequency ranges. However, experiments performed at infrared or terahertz (THz) frequencies have so far only occurred at two extremes of the phase diagram, either in zero applied magnetic field 30,35 or in large pulsed magnetic fields of order µ 0 H ≈ 10T 36 .…”

Section: Introductionmentioning

confidence: 99%

Low-energy magnon dynamics and magneto-optics of the skyrmionic Mott insulator Cu2OSeO3

et al. 2017

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In this work, we present a comprehensive study of the low energy optical magnetic response of the skyrmionic Mott insulator Cu2OSeO3 via high resolution time-domain THz spectroscopy. In zero field, a new magnetic excitation (f0 = 2.03 THz) which has not been predicted by spin-wave theory is observed and shown, with accompanying time-of-flight neutron scattering experiments, to be a zone folded magnon from the R to Γ points of the Brillouin zone. Highly sensitive polarimetry experiments performed in weak magnetic fields, µ0H < 200 mT, observe Faraday and Kerr rotations which are proportional to the sample magnetization, allowing for optical detection of the skyrmion phase and construction of a magnetic phase diagram. From these measurements, we extract a critical exponent of β = 0.35 ± 0.04, in good agreement with the expected value for the 3D Heisenberg universality class of β = 0.367. In large magnetic fields, µ0H > 5 T, we observe the magnetically active uniform mode of the ferrimagnetic field polarized phase whose dynamics as a function of field and temperature are studied. In addition to extracting a g eff = 2.08 ± 0.03, we observe the uniform mode to decay through a non-Gilbert damping mechanism and to possesses a finite spontaneous decay rate, Γ0 ≈ 25 GHz, in the zero temperature limit. Our observations are attributed to Dzyaloshinkii-Moriya interactions, which have been proposed to be exceptionally strong in Cu2OSeO3 and are expected to impact the low energy magnetic response of such chiral magnets.

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“…Called non-reciprocal directional dichroism (NDD), absorption asymmetry was first observed by Hopfield and Thomas 29 over 50 years ago in CdS. Much more recently, the precise symmetry requirements for NDD in magnetic materials were systematically investigated by Szaller et al [30]. Strong NDD is expected for the spin excitations of multiferroic materials when both time reversal and spatial inversion symmetries are broken by the spin state.…”

Section: Introductionmentioning

confidence: 99%

Spin-induced polarizations and nonreciprocal directional dichroism of the room-temperature multiferroicBiFeO3

et al. 2015

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A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as non-reciprocal directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the non-reciprocal directional dichroism in BiFeO3 is dominated by the spincurrent polarization and is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the non-reciprocal directional dichroism observed for magnetic field along [1, −1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. Our work demonstrates that an analysis of the non-reciprocal directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.

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Symmetry conditions for nonreciprocal light propagation in magnetic crystals

Cited by 84 publications

References 61 publications

One-way transparency of four-coloured spin-wave excitations in multiferroic materials

One-way transparency of four-coloured spin-wave excitations in multiferroic materials

Low-energy magnon dynamics and magneto-optics of the skyrmionic Mott insulator Cu2OSeO3

Spin-induced polarizations and nonreciprocal directional dichroism of the room-temperature multiferroicBiFeO3

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