56 research outputs found
Classification of atomic-scale multipoles under crystallographic point groups and application to linear response tensors
Four types of atomic-scale multipoles, electric, magnetic, magnetic toroidal,
and electric toroidal multipoles, give a complete set to describe arbitrary
degrees of freedom for coupled charge, spin, and orbital of electrons. We here
present a systematic classification of these multipole degrees of freedom
towards the application in condensed matter physics. Starting from the
multipole description under the rotation group in real space, we generalize the
concept of multipoles in momentum space with the spin degree of freedom. We
show how multipoles affect the electronic band structures and linear responses,
such as the magneto-electric effect, magneto-current (magneto-gyrotropic)
effect, spin conductivity, Piezo-electric effect, and so on. Moreover, we
exhibit a complete table to represent the active multipoles under 32
crystallographic point groups. Our comprehensive and systematic analyses will
give a foundation to identify enigmatic electronic order parameters and a guide
to evaluate peculiar cross-correlated phenomena in condensed matter physics
from microscopic point of view.Comment: 37 pages, 4 figures, 32 table
High-performance descriptor for magnetic materials:Accurate discrimination of magnetic symmetries
The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP) providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher order
partial spectrum is required in general to characterize detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from first-principles calculations without spin-orbit coupling. We apply the
present method to the symmetry-classified magnetic structures for the crystals
of MnIr and MnSn, which are known to exhibit anomalous transport under
the antiferromagnetic order, and examine the discrimination performance of the
descriptor for different magnetic structures on the same crystal.Comment: 13 pages including supplementary information, 8 figure
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