186 research outputs found
Effect of magnetic anisotropy on Skyrmions with a high topological number in itinerant magnets
We report our numerical results for the effect of magnetic anisotropy on a
Skyrmion crystal with a high topological number of two, which was recently
discovered in an itinerant electron model [R. Ozawa, S. Hayami, and Y. Motome,
Phys. Rev. Lett. 118, 147205 (2017)]. By performing numerical simulations based
on the kernel polynomial method and the Langevin dynamics for the Kondo lattice
model on a triangular lattice, we find that the topological property remains
robust against the single-ion anisotropy, while the magnetic texture is
deformed continuously. The resultant spin structure is characterized by three
wave numbers (triple- state), in which the component of spins forms a
magnetic vortex crystal and the component of spins behaves a sinusoidal
wave. For larger anisotropy, we show that the system exhibits a phase
transition from the Skyrmion crystal to topologically trivial phases with
vanishing scalar chirality: a single- collinear and double- noncoplanar
states for the easy-axis and easy-plane anisotropy, respectively. We also
examine the effect of the single-ion anisotropy in an external magnetic field,
and find that the field range of the Skyrmion crystal is rather insensitive to
the anisotropy, in contrast to another Skyrmion crystal with the topological
number of one whose field range is considerably extended (reduced) by the
easy-axis (easy-plane) anisotropy.Comment: 7 pages, 5 figure
Chern insulating state with double- ordering wave vectors at the Brillouin zone boundary
Magnetic multiple- states consisting of multiple spin density waves are a
source of unconventional topological spin textures, such as skyrmion and
hedgehog. We theoretically investigate a topologically nontrivial double-
state with a net spin scalar chirality on a two-dimensional square lattice. We
find that a double- spiral superposition of the ordering wave vectors
located at the Brillouin zone boundary gives rise to unconventional noncoplanar
spin textures distinct from the skyrmion crystal. We show that such a
double- state is stabilized by the interplay among the easy-axis anisotropic
interaction, high-harmonic wave-vector interaction, and external magnetic
field. Furthermore, the obtained double- state becomes a Chern insulating
state with a quantum Hall conductivity when the Fermi level is located in the
band gaps. Our present results provide another platform to realize topological
magnetic states other than skyrmion crystals by focusing on the symmetry of
constituent ordering wave vectors in momentum space.Comment: 11 pages, 11 figure
Classification of multipoles induced by external fields and currents under electronic nematic ordering with quadrupole moments
We theoretically investigate the effect of external fields and currents on
electronic nematic orderings based on the concept of augmented multipoles
consisting of electric, magnetic, magnetic toroidal, and electric toroidal
multipoles. We show the relation between rank-2 electric quadrupoles and the
other multipoles, the former of which corresponds to the microscopic order
parameter for the nematic phases. The electric (magnetic) field induces the
rank-1 and rank-3 electric (magnetic) multipoles and rank-2 electric toroidal
(magnetic toroidal) quadrupoles, while the electric current induces the rank-1
and rank-3 magnetic toroidal multipoles and rank-2 magnetic quadrupoles. We
classify the active multipoles under magnetic point groups, which will be a
reference to explore cross-correlation and transport phenomena in nematic
phases.Comment: 7 pages, 1 figure, 7 table
Emergent odd-parity multipoles and magnetoelectric effects on a diamond structure: implication to 5 transition metal oxides OsO ( K, Rb, and Cs)
We report our theoretical predictions on the linear magnetoelectric (ME)
effects originating from odd-parity multipoles associated with spontaneous spin
and orbital ordering on a diamond structure. We derive a two-orbital model for
electrons in orbitals by including the effective spin-orbit coupling
which arises from the mixing between and orbitals. We show that
the model acquires a net antisymmetric spin-orbit coupling once staggered spin
and orbital orders occur spontaneously. The staggered orders are accompanied by
odd-parity multipoles: magnetic monopole, quadrupoles, and toroidal dipoles. We
classify the types of the odd-parity multipoles according to the symmetry of
the spin and orbital orders. Furthermore, by computing the ME tensor using the
linear response theory, we show that the staggered orders induce a variety of
the linear ME responses. We elaborate all possible ME responses for each
staggered order, which are useful to identify the order parameter and to detect
the odd-parity multipoles by measuring the ME effects. We also elucidate the
effect of lowering symmetry by a tetragonal distortion, which leads to richer
ME responses. The implications of our results are discussed for transition
metal oxides, OsO ( K, Rb, and Cs), in which the order parameters
are not fully identified.Comment: 11 pages, 2 figures, 3 table
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