Non-reciprocal Linear Dichroism Research Articles

Imaging switchable magnetoelectric quadrupole domains via nonreciprocal linear dichroism

Parity-odd magnetoelectric multipoles such as magnetic quadrupoles and toroidal dipoles contribute to various symmetry-dependent magnetic phenomena and formation of exotic ordered phases. However, the observation of domain structures emerging due to symmetry breaking caused by these multipoles is a severe challenge because of their antiferromagnetic nature without net magnetization. Here, we report the discovery of nonreciprocal linear dichroism for visible light (~4% at 1.8 eV) in a magnetic quadrupole ordered phase of antiferromagnetic Pb(TiO)Cu4(PO4)4, which enables the identification of magnetic quadrupole domains of opposite signs. Symmetry considerations indicate that nonreciprocal linear dichroism is induced by the optical magnetoelectric effect, i.e., the linear magnetoelectric effect for electromagnetic waves. Using the nonreciprocal linear dichroism, we successfully visualize spatial distributions of quadrupole domains and their isothermal electric-field switching by means of a transmission-type polarized light microscope. The present work exemplifies that the optical magnetoelectric effect efficiently visualizes magnetoelectric multipole domains responding to external perturbations.

Atomic Theory of Parity-Odd (E1–M1) Photon Absorption Event

Light scattering proceeding through electric and magnetic dipole absorption events (E1–M1) exhibits natural circular dichroism, widely used in the characterization of chiral media, and the magneto-chiral effect, which is under consideration as a mechanism for the homo-chirality of life. Additional manifestations of E1–M1 scattering are resonance enhanced Bragg diffraction and non-reciprocal linear dichroism. In spite of its established importance for a raft of significant phenomena, there has not been a complete treatment of E1–M1 light scattering by electrons. Starting from the interaction that includes both electron spin and angular momentum variables, we construct scattering that proceeds via a spin–orbit split intermediate state for the photo-ejected electron. Employing new relations for re-coupling angular momentum we give a theoretical basis for the derivation of sum-rules for integrated dichroic signals. In order to assist in the interpretation of the algebraic terms present for E1–M1 we construct ...

Quantum theory of natural circular, magneto-chiral and non-reciprocal linear dichroism

For dichroic signals produced by parity-odd absorption events, we expose, in correct and concise form, electron degrees of freedom that participate in correlations between spin and orbital variables. Additionally, and for the first time, we prove sum rules for integrated dichroic signals, analogous to the celebrated work by Thole et al (1992 Phys. Rev. Lett. 68 1943) for parity-even events. Natural circular dichroism is a standard method for characterizing chiral materials, and the photon magneto-chiral effect is an important candidate for the origin of the homo-chirality of life.

On the Nature of the Magnetic Ground-State Wave Function of V2O3

After a brief historical introduction, we dwell on two recent experiments in the low-temperature, monoclinic phase of V2O3: K-edge resonant x-ray scattering and non-reciprocal linear dichroism, whose interpretations are in conflict, as they require incompatible magnetic space groups. Such a conflict is critically reviewed, in the light of the present literature, and new experimental tests are suggested, in order to determine unambiguously the magnetic group. We then focus on the correlated, non-local nature of the ground-state wave function, that is at the basis of some drawbacks of the LDA + U approach: we singled out the physical mechanism that makes LDA + U unreliable, and indicate the way out for a possible remedy. Finally we explain, by means of a symmetry argument related to the molecular wave function, why the magnetic moment lies in the glide plane, even in the absence of any local symmetry at vanadium sites.

Second-order magnetoelectric susceptibility in the optical region: The case of boraciteCu3B7O13Br

In the cubic phase of boracite ${\mathrm{Cu}}_{3}{\mathrm{B}}_{7}{\mathrm{O}}_{13}\mathrm{Br}$ (symmetry class ${T}_{d})$ the anisotropy and dispersion of nonreciprocal linear dichroism (ND) and nonreciprocal linear birefringence (NB) have been studied. The two magnetic-field-induced effects belong to the class of spatial dispersion phenomena. They have been observed near to the two strong absorption bands at the photon energies ${E}_{01}=1.5\mathrm{eV}$ and ${E}_{02}=1.2\mathrm{eV}.$ ${E}_{01}$ and ${E}_{02}$ are assigned to electronic transitions from the singlet ground state ${}^{2}{\mathrm{B}}_{2}$ to states of the doublet ${}^{2}E.$ The analysis of dispersion of ND and NB is based on the crystal-field theory whereby spin-orbit coupling and Zeeman interaction have been included. An adequate description is obtainable only if the symmetry of the crystal field at ${\mathrm{Cu}}^{2+}$ ions is lower than tetragonal. Two mechanisms are discussed as the origin of symmetry reduction. At first, a structural disorder of halogen and/or metal ions in the boracite crystal lattice produces low-symmetry components of the crystal field and these components split the excited state ${}^{2}E.$ Second, symmetry is reduced by the dynamic Jahn-Teller effect.

Second Order Magnetoelectric Susceptibility in the Optical Region

The physical phenomena related to manifestation of the second order magnetoelectric susceptibility in optical region are considered. In magnetoelectrics of the type EB 2 this susceptibility contributes to magneto-induced spatial dispersion optical phenomena such as a non-reciprocal birefringence or a non-reciprocal linear dichroism. The analysis of experimental data in boracite and rare-earth sesquisulphide single crystals shows that the magnetoelectric mechanism is the basic one in formation of these phenomena. In magnetic semiconductors type Cd 1 m x Mn x Te the magnetoelectric effect results in the frequency independent part of non-reciprocal birefringence. The results of the theoretical treatment of the second order magnetoelectric susceptibility in the optical region are presented.

Application of the high-accuracy universal polarimeter to magnetic and absorbing crystals

In this paper we show that the high-accuracy universal polarimeter can be used to investigate the optical properties of (almost) any crystal through which light can be transmitted. The only extra condition is that the reciprocal linear birefringence (or the reciprocal linear dichroism) of the sample is large with respect to the other optical effects that are present. The sample is allowed to exhibit reciprocal linear birefringence and reciprocal circular birefringence. This is the situation for which the high-accuracy universal polarimeter was originally intended. We show, however, that reciprocal linear dichroism and reciprocal circular dichroism may also be present. The method can, therefore, be applied to (weakly) absorbing crystals. Furthermore, optical effects are taken into account that are related to the breaking of time-reversal symmetry. These are the non-reciprocal circular birefringence, non-reciprocal circular dichroism, non-reciprocal linear birefringence and non-reciprocal linear dichroism. This means that, under some conditions, each (weakly) absorbing, magnetic crystal can be investigated with the high-accuracy universal polarimeter. We derive a unified formula for the intensity change of the light that propagates through the polarimeter. This expression can be used to determine the (complex) eigenpolarizations of an arbitrary sample. Moreover, it is shown how this unified formula can be translated to a formula in terms of the different birefringent and dichroic optical effects. The relevant formula for a specific case can, therefore, be given directly. The method is demonstrated by means of measurements on samples of NiSO4.6H2O. This material shows reciprocal linear birefringence, reciprocal linear dichroism, reciprocal circular birefringence and reciprocal circular dichroism, simultaneously.