Abstract
Background: Magnetoelectric multipoles, which break both space-inversion and time-reversal symmetries, play an important role in the magnetoelectric response of a material. Motivated by uncovering the underlying fundamental physics of the magnetoelectric multipoles and the possible technological applications of magnetoelectric materials, understanding as well as detecting such magnetoelectric multipoles has become an active area of research in condensed matter physics. Here we employ the well-established Compton scattering effect as a possible probe for the magnetoelectric toroidal moments in LiNiPO4. Methods: We employ combined theoretical and experimental techniques to compute as well as detect the antisymmetric Compton profile in LiNiPO4. For the theoretical investigation we use density functional theory to compute the anti-symmetric part of the Compton profile for the magnetic and structural ground state of LiNiPO4. For the experimental verification, we measure the Compton signals for a single magnetoelectric domain sample of LiNiPO4, and then again for the same sample with its magnetoelectric domain reversed. We then take the difference between these two measured signals to extract the antisymmetric Compton profile in LiNiPO4. Results: Our theoretical calculations indicate an antisymmetric Compton profile in the direction of the ty toroidal moment in momentum space, with the computed antisymmetric profile around four orders of magnitude smaller than the total profile. The difference signal that we measure is consistent with the computed profile, but of the same order of magnitude as the statistical errors and systematic uncertainties of the experiment. Conclusions: While the weak difference signal in the measurements prevents an unambiguous determination of the antisymmetric Compton profile in LiNiPO4, our results motivate further theoretical work to understand the factors that influence the size of the antisymmetric Compton profile, and to identify materials exhibiting larger effects.
Highlights
Magnetoelectric (ME) multipoles are key to understanding the linear ME response in solids, in which an applied electric field induces a linear order magnetization, and vice versa.∫ M In ijp=artirciuμlja(rr, )tdh3er1s,2e,cownhde-rraenkμ (Mr )Eismtuhletipmolaegnteentiszoart,iodnefdineendsitays, has the same symmetry as the linear ME response tensor
While the weak difference signal in the measurements prevents an unambiguous determination of the antisymmetric Compton profile in LiNiPO4, our results motivate further theoretical work to understand the factors that influence the size of the antisymmetric Compton profile, and to identify materials exhibiting larger effects
In agreement with the expectation from symmetry arguments, we find an antisymmetric component in the Compton profile only along the y direction, which is the direction of the toroidal moment ty, in momentum space
Summary
∫ M In ijp=artirciuμlja(rr, )tdh3er1s,2e,cownhde-rraenkμ (Mr )Eismtuhletipmolaegnteentiszoart,iodnefdineendsitays, has the same symmetry as the linear ME response tensor. Both are only non-zero when space-inversion (I ) and timereversal (T ) symmetries are broken simultaneously, and there is a one-to-one correlation between their components. Materials with an antisymmetric off-diagonal linear ME response have non-zero antisymmetric off-diagonal elements in their Mij tensor[3]. This proposal motivated considerable interest in ME toroidal moments in solids, leading to experimental efforts to detect them using resonant x-ray diffraction[6,7,8,9,10], magneto chiral dichroism[11,12], and optical measurements[13], as well as to image ferrotoroidic domains[5]. We employ the well-established Compton scattering effect as a possible probe for the magnetoelectric toroidal moments in LiNiPO4
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