Satoru Hayami

Toroidal order in metals without local inversion symmetry

The hallmark of the toroidal order

Spontaneous parity breaking in spin-orbital coupled systems

\mathbf{T}

Bubble and Skyrmion Crystals in Frustrated Magnets with Easy-Axis Anisotropy

in solids is the presence of the cross-coupling term

Spontaneous Multipole Ordering by Local Parity Mixing

\mathbf{T}\ensuremath{\cdot}(\mathbf{H}\ifmmode\times\else\texttimes\fi{}\mathbf{E})

Frustration and chiral orderings in correlated electron systems.

in the free energy of the system that leads to antisymmetric magneto-electric effect. In the last several years toroidal order has attracted interest in connection with multiferroic insulating materials. The authors of this manuscript show that such an exotic order can occur even in metallic systems on lattice structures where the spatial-inversion symmetry is preserved globally but broken intrinsically at each magnetic site. They suggest a uranium compound UNi

Emergent spin-valley-orbital physics by spontaneous parity breaking.

{}_{4}

Zero-Field Skyrmions with a High Topological Number in Itinerant Magnets

B as a candidate material where such a state can be realized.

Asymmetric magnon excitation by spontaneous toroidal ordering

Effects of spontaneous parity breaking by charge, spin, and orbital orders are investigated in a two-band Hubbard model on a honeycomb lattice. This is a minimal model in which the interorbital hopping, atomic spin-orbit coupling, and strong electron correlation give rise to fascinating properties, such as the magnetoelectric effects, quantum spin Hall effect, and spin or valley splitting in the band structure. We perform the symmetry analysis of possible broken-parity states and the mean-field analysis of their competition. We find that the model at 1/4 filling exhibits a spin-orbital composite ordered state and a charge ordered state, in addition to a paramagnetic quantum spin Hall insulator. We show that the composite ordered phase exhibits two types of magnetoelectric responses. The charge ordered state shows spin splitting in the band structure, while the topological nature varies depending on electron correlations.

Partial Disorder in the Periodic Anderson Model on a Triangular Lattice

We clarify the conditions for the emergence of multiple-Q structures out of lattice and easy-axis spin anisotropy in frustrated magnets. By considering magnets whose exchange interaction has multiple global minima in momentum space, we find that both types of anisotropy stabilize triple-Q orderings. Moderate anisotropy leads to a magnetic field-induced skyrmion crystal, which evolves into a bubble crystal for increasing spatial and spin anisotropy. Finally, the bubble crystal exhibits a quasi-continuous (devil’s staircase) temperature dependent ordering wave-vector, characteristic of the competition between frustrated exchange and strong easy-axis anisotropy.

Effective bilinear-biquadratic model for noncoplanar ordering in itinerant magnets

Broken spatial inversion symmetry in spin–orbital coupled systems leads to a mixing between orbitals with different parity, which results in unusual electronic structures and transport properties. ...