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Satoru Hayami

Publications and source records attributed to Satoru Hayami.

At least 91 records · Page 5Linked to original sources
arXiv2023

Unconventional Hall effect and magnetoresistance induced by metallic ferroaxial ordering

Transport property under metallic ferroaxial ordering in an external magnetic field is theoretically investigated. After presenting the relation between the magnetoconductivity tensor and ferroaxial moment from the symmetry viewpoint, we analyze the behavior of the unconventional Hall effect and magnetoconductivity for a general five $d$-orbital tight-binding model under the point group $C_{\rm 4h}$, where the ferroaxial moment is activated. We show that the crystalline electric field that arises from the symmetry reduction from $D_{\rm 4h}$ to $C_{\rm 4h}$ is essential for the ferroaxial-related magnetotransport, while the relativistic spin-orbit coupling is not required. We also compare the unconventional Hall effect driven by the ferroaxial moment with the conventional Hall effect, the latter of which does not require the ferroaxial moment. The present results provide characteristic transport properties in the ferroaxial systems, which can be observed in various candidate materials like Ca$_5$Ir$_3$O$_{12}$.

cond-mat.str-el↗
arXiv2023

Uniform and Staggered electric axial moment in zigzag chain

We theoretically investigate electronic orderings with the electric axial moment without breakings of both spatial inversion and time-reversal symmetries in the zigzag-chain system. Especially, we elucidate the role of the local odd-parity hybridization arising from locally noncentrosymmetric lattice structures based on symmetry and microscopic model analyses. We show that the odd-parity crystalline electric field gives rise to an effective cross-product coupling between the electric dipole and electric toroidal dipole, the latter of which corresponds to the electric axial moment. As a result, the staggered component of the electric axial moment is induced by applying an external electric field, while its uniform component is induced via the appearance of staggered electric dipole ordering. We also show that uniform electric quadrupole ordering accompanies uniform electric axial moment. Furthermore, we discuss transverse magnetization as a consequence of the orderings with the uniform electric axial moment. Our results extend the scope of materials exhibiting electric axial ordering to those with locally noncentrosymmetric lattice structures.

cond-mat.str-el↗
arXiv2023

Checkerboard bubble lattice formed by octuple-period quadruple-$Q$ spin density waves

We investigate multiple-$Q$ instability on a square lattice at particular ordering wave vectors. We find that a superposition of quadruple-$Q$ spin density waves, which are connected by fourfold rotational and mirror symmetries, gives rise to a checkerboard bubble lattice with a collinear spin texture as a result of the geometry among the constituent ordering wave vectors in the Brillouin zone. By performing the simulated annealing for a fundamental spin model, we show that such a checkerboard bubble lattice is stabilized under an infinitesimally small easy-axis two-spin anisotropic interaction and biquadratic interaction at zero field, while it is degenerate with an anisotropic double-$Q$ state in the absence of the biquadratic interaction. The obtained multiple-$Q$ structures have no intensities at high-harmonic wave vectors in contrast to other multiple-$Q$ states, such as a magnetic skyrmion lattice. We also show that the checkerboard bubble lattice accompanies the charge density wave and exhibits a nearly flat band dispersion in the electronic structure. Our results provide another route to realize exotic multiple-$Q$ spin textures by focusing on the geometry and symmetry in terms of the wave vectors in momentum space.

cond-mat.str-el↗
arXiv2023

Chern insulating state with double-$Q$ ordering wave vectors at the Brillouin zone boundary

Magnetic multiple-$Q$ 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-$Q$ state with a net spin scalar chirality on a two-dimensional square lattice. We find that a double-$Q$ 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-$Q$ 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-$Q$ 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.

cond-mat.str-el↗
arXiv2023

Antiferro skyrmion crystal phases in a synthetic bilayer antiferromagnet under an in-plane magnetic field

We theoretically propose a generation of an antiferro skyrmion crystal (AF-SkX) in a synthetic bilayer antiferromagnetic system under an external magnetic field. By performing the simulated annealing for a spin model on a centrosymmetric bilayer triangular lattice, we find that the interplay among the layer-dependent Dzyaloshinskii-Moriya interaction, the easy-plane single-ion anisotropy, the interlayer exchange interaction, and the in-plane magnetic field leads to instability toward the AF-SkX. The obtained AF-SkX consists of the skyrmion layer and anti-skyrmion layer with opposite skyrmion numbers, which results in no skyrmion number as well as spin scalar chirality in the whole system. We also show that a ferri-type skyrmion crystal, where one of the layers has the skyrmion number of one and the other does not, appears when the magnitude of the magnetic field is varied. Our results provide a guideline to experimentally search for the AF-SkX in bulk and layered materials.

cond-mat.str-el↗
arXiv2023

Field-direction-dependent skyrmion crystals in noncentrosymmetric cubic magnets: A comparison between point groups $(O,T)$ and $T_{\rm d}$

We investigate the instability toward a skyrmion crystal (SkX) in noncentrosymmetric cubic magnets with an emphasis on a comparison between point groups $(O,T)$ and $T_{\rm d}$. By constructing low-temperature magnetic phase diagrams under an external magnetic field for three directions based on numerically simulated annealing, we find that the system under the point group $(O,T)$ exhibits different two types of SkXs depending on the field direction, while that under $T_{\rm d}$ does not show such an instability. The difference between them is understood from the difference in the momentum-dependent Dzyaloshinskii-Moriya interaction under each point group. Meanwhile, we show that the system under $T_{\rm d}$ leads to the SkX instability by considering an additional effect of the uniaxial strain, which lowers the symmetry to $D_{\rm 2d}$. We obtain two different SkXs: Néel-type and anti-type SkXs, the former of which is stabilized in the presence of the interactions at the three-dimensional ordering wave vectors. The present results provide rich topological spin textures in the three-dimensional systems, which are sensitive to the magnetic-field direction and point-group symmetry.

cond-mat.str-el↗
arXiv2023

Magnetic bubble crystal in tetragonal magnets

A magnetic bubble crystal is a two-dimensional soliton lattice consisting of multiple spin density waves similar to a magnetic skyrmion crystal. Nevertheless, the emergence of the bubble crystal with a collinear spin texture is rare compared to that of the skyrmion crystal with a noncoplanar spin texture. Here we theoretically report the stabilization mechanisms of the bubble crystal in tetragonal magnets. By performing numerical calculations based on an efficient steepest descent method for an effective spin model with magnetic anisotropy and multiple spin interactions in momentum space on a two-dimensional square lattice, we construct magnetic field-temperature phase diagrams for various sets of model parameters. We find that the bubble crystal is stabilized at finite temperatures near the skyrmion crystal by an easy-axis anisotropic two-spin interaction. Through a detailed analysis, we also show that the high-harmonic wave-vector interaction and the biquadratic interaction play important roles in the stability of the bubble crystal. Our results indicate a close relationship between the bubble crystal and the skyrmion crystal in terms of the stabilization mechanisms, which suggests the possibility of the bubble crystal in the skyrmion-hosting materials by controlling the easy-axis magnetic anisotropy through external and/or chemical pressure.

cond-mat.str-el↗
arXiv2023

Symmetry-adapted modeling for molecules and crystals

We have developed a symmetry-adapted modeling procedure for molecules and crystals. By using the completeness of multipoles to express spatial and time-reversal parity-specific anisotropic distributions, we can generate systematically the complete symmetry-adapted multipole basis set to describe any of electronic degrees of freedom in isolated cluster systems and periodic crystals. The symmetry-adapted modeling is then achieved by expressing the Hamiltonian in terms of the linear combination of these bases belonging to the identity irreducible representation, and the model parameters (linear coefficients) in the Hamiltonian can be determined so as to reproduce the electronic structures given by the density-functional computation. We demonstrate our method for the modeling of graphene, and emphasize usefulness of the symmetry-adapted basis to analyze and predict physical phenomena and spontaneous symmetry breaking in a phase transition. The present method is complementary to de-facto standard Wannier tight-binding modeling, and it provides us with a fundamental basis to develop a symmetry-based analysis for materials science.

cond-mat.mtrl-sci↗
arXiv2023

Microscopic mechanism for intrinsic nonlinear anomalous Hall conductivity in noncollinear antiferromagnetic metals

We theoretically investigate an intrinsic nonlinear anomalous Hall effect (INAHE) in space-time ($\mathcal{PT}$) symmetric antiferromagnetic metals. The INAHE is characterized by an asymmetric and non-dissipative part of the second-order electric conductivity tensor in the clean limit in contrast to the Drude-type symmetric conductivity tensor with dissipation. By introducing a multipole description, we show that the emergence of the INAHE is due to active odd-parity magnetic quadrupoles or magnetic toroidal dipoles under magnetic orderings. In order to clarify the microscopic origin of the INAHE, we specifically consider a fundamental tight-binding model of a three-dimensional tetragonal system. We demonstrate that the INAHE arises from the effective coupling between magnetic ordering and antisymmetric spin--orbit interaction. We also discuss essential electron hopping paths driving the INAHE.

cond-mat.str-el↗
arXiv2023

Nonlinear Transverse Magnetic Susceptibility under Electric Toroidal Dipole Ordering

An electric toroidal dipole (ETD) moment is one of the fundamental dipole moments as well as electric and magnetic ones. Although it directly couples to neither an electric nor magnetic field due to its spatial inversion and time-reversal parities, its ordered state leads to unconventional transverse responses of the conjugate physical quantities. We here theoretically investigate nonlinear transverse magnetic susceptibility under the ETD ordering. By performing a self-consistent mean-field calculation for a five $d$-orbital model under a tetragonal crystalline electric field and using the nonlinear Kubo formula, we show that a third-order transverse magnetic susceptibility corresponding to a uniform magnetization perpendicular to the external magnetic field becomes nonzero once the ETD moment is ordered under tetragonal crystalline electric field. Moreover, we find that spin-orbital entanglement and a low-lying first excited crystal-field level are important for realizing large transverse responses.

cond-mat.str-el↗
arXiv2023

Chiral charge as hidden order parameter in URu$_2$Si$_2$

We propose a chiral charge (electric toroidal monopole) as the hidden order parameter in URu$_{2}$Si$_{2}$, which satisfies all the symmetry conditions accumulated by many experimental and theoretical efforts since its discovery. By using the minimal effective $d$-$f$ hybridized model in the itinerant picture, we demonstrate expected cross-correlated phenomena under the chiral charge ordering, and spatial distribution of the order parameter with surface or domain boundary. Based on the results, we discuss possible experiments by using NQR and diffraction measurements under an electric field, or optical measurements near the surface or domain boundary, although the proposed fully rotational symmetric order parameter is hard to detect as it is.

cond-mat.str-el↗
arXiv2023

Multiple-$q$ dipole-quadrupole instability in spin-1 triangular-lattice systems

We investigate a mechanism of multiple-$q$ states consisting of magnetic dipole and electric quadrupole degrees of freedom in spin-1 triangular-lattice systems. By systematically analyzing a minimal effective multipole model with bilinear multipole-multipole interactions in momentum space on a triangular lattice, we find minimum conditions of multipole interactions leading to the multiple-$q$ instability at zero temperature even without single-ion magnetic anisotropy and higher-order interactions. We present six types of triple-$q$ states with different magnetic dipole and electric quadrupole configurations depending on the model parameters. Our results indicate that the interplay between dipole and quadrupole degrees of freedom provides another source of inducing rich multiple-$q$ states.

cond-mat.str-el↗
arXiv2023

Symmetry analysis of light-induced magnetic interactions via Floquet engineering

Anisotropic magnetic interactions become the origins of intriguing magnetic structures, such as helical and skyrmion structures by the Dzyaloshinskii-Moriya interaction. In general, possible anisotropic exchange interactions are restricted by crystal symmetry. Meanwhile, by lowering the crystal symmetry with light, additional anisotropic magnetic interactions are expected according to its polarization and frequency. In this study, we clarify a relationship between anisotropic magnetic interactions and symmetry lowering in insulating magnets irradiated by light. Based on the Floquet formalism, we find that a variety of anisotropic two-spin and three-spin interactions are induced via spin-dependent electric polarizations activated by light irrespective of the presence/absence of the spatial inversion symmetry; we systematically classify them in the hexagonal point group, tetragonal point group, and their subgroups. Our symmetry analyses show that the light-induced two-spin (three-spin) interaction is owing to the reduction of the point group to a chiral point group (black and white magnetic point group). We also demonstrate the effect of the light-induced magnetic interactions on the magnetic structures in a triangular unit. Our results will be a symmetry-based reference for the Floquet engineering of magnetic structures.

cond-mat.str-el↗
arXiv2023

Cluster Toroidal Multipoles Formed by Electric-Quadrupole and Magnetic-Octupole Trimers: A Possible Scenario for Hidden Orders in Ca$_5$Ir$_3$O$_{12}$

Cluster multipole orderings composed of atomic high-rank multipole moments are theoretically investigated with a 5$d$-electron compound Ca$_5$Ir$_3$O$_{12}$ in mind. Ca$_5$Ir$_3$O$_{12}$ exhibits two hidden orders: One is an intermediate-temperature phase with time-reversal symmetry and the other is a low-temperature phase without time-reversal symmetry. By performing the symmetry and augmented multipole analyses for a $d$-orbital model under the hexagonal point group $D_{\rm 3h}$, we find that the 120$^{\circ}$-type ordering of the electric quadrupole corresponds to cluster electric toroidal dipole ordering with the electric ferroaxial moment, which can become the microscopic origin of the intermediate-temperature phase in Ca$_5$Ir$_3$O$_{12}$. Furthermore, based on ${}^{193}$Ir synchrotron-radiation-based Mössbauer spectroscopy, we propose that the low-temperature phase in Ca$_5$Ir$_3$O$_{12}$ is regarded as a coexisting state with cluster electric toroidal dipole and cluster magnetic toroidal quadrupole, the latter of which is formed by the 120$^{\circ}$-type ordering of the magnetic octupole and accompanies a small uniform magnetization as a secondary effect. Our results provide a clue to two hidden phases in Ca$_5$Ir$_3$O$_{12}$.

cond-mat.str-el↗
arXiv2023

Anisotropic spin model and multiple-$Q$ states in cubic systems

Multiple-$Q$ states manifest themselves in a variety of noncollinear and noncoplanar magnetic structures depending on the magnetic interactions and lattice structures. In particular, cubic-lattice systems can host a plethora of multiple-$Q$ states, such as magnetic skyrmion and hedgehog lattices. We here classify momentum-dependent anisotropic exchange interactions in the cubic-lattice systems based on the magnetic representation analysis. We construct an effective spin model for centrosymmetric cubic space groups, $Pm\bar{3}m$ and $Pm\bar{3}$, and noncentrosymmetric ones, $P\bar{4}3m$, $P432$, and $P23$: The former include the symmetric anisotropic exchange interaction, while the latter additionally include the Dzyaloshinskii-Moriya interaction. We demonstrate that the anisotropic exchange interaction becomes the origin of the multiple-$Q$ states by applying the anisotropic spin model to the case under $Pm\bar{3}$. We show several multiple-$Q$ instabilities in the ground state by performing simulated annealing. Our results will be a reference for not only exploring unknown multiple-$Q$ states but also understanding the origin of the multiple-$Q$ states observed in both noncentrosymmetric and centrosymmetric magnets like EuPtSi and SrFeO$_3$.

cond-mat.str-el↗
arXiv2023

Stacking-dependent nonreciprocal transport in magnetic skyrmions

I theoretically propose an emergence of nonlinear nonreciprocal transport in centrosymmetric magnets with topological spin textures. By focusing on the stacking degree of freedom of the skyrmion crystals on a layered triangular lattice, I find that the ABC-stacking structure of the skyrmion crystals gives rise to out-of-plane nonreciprocal transport without the relativistic spin-orbit coupling. I show that such nonreciprocal transport is caused by an asymmetric band modulation due to the stacking structure, where the scalar chirality across the layers is a key ingredient. I also show an effective spin model to stabilize the ABC-stacking skyrmion structure. The present results indicate that the stacking structure of the skyrmion crystal becomes a source of further intriguing transport properties.

cond-mat.mes-hall↗
arXiv2022

Mean-field Study of Antiferromagnetic and Antiferroquadrupolar Orderings in Tetragonal CeCoSi

We investigate the stability of the multipolar orderings in $f$-electron material CeCoSi based on a self-consistent mean-field calculation for the effective localized model. This material has two ordered phases in the temperature-pressure phase diagram: the antiferromagnetic phase and the nonmagnetic phase, the latter of which has been suggested to be an antiferroquadrupolar phase. Meanwhile, the origin of the antiferroquadrupolar phase has been unclear, since a quadrupole degree of freedom is present only between the ground-state level and highly separated excited-state level under a tetragonal crystalline electric field (CEF), whose energy scale is much larger than the transition temperature. To understand the sequence of the phase transition from the paramagnetic phase, antiferroquadrupolar phase, and antiferromagnetic phase when decreasing the temperature, we examine the important interaction parameters in the effective localized model. We clarify that the $3z^2-r^2$-type of the antiferroquadrupolar interactions can renormalize the CEF level splitting, which assists a quadrupolar ordering even in a tetragonal system without orbital degeneracy. Moreover, the stability of the antiferroquadrupolar and antiferromagnetic states in a magnetic field and the behavior of the magnetic/quadrupolar susceptibility are also presented for the information to identify the unknown order parameter in the nonmagnetic ordered phase.

cond-mat.str-el↗
arXiv2022

Ferroaxial moment induced by vortex spin texture

The nature of an electric ferro-axial moment characterizing a time-reversal-even axial-vector quantity is theoretically investigated under magnetic orderings. We clarify that a vortex spin texture results in the emergence of the ferro-axial moment depending on the helicity. By introducing a multipole description, we show that the ferro-axial nature appears when two types of odd-parity magnetic multipoles become active under the vortex spin texture: One is the magnetic monopole and the other is the magnetic toroidal dipole. We present all the magnetic point groups to possess the ferro-axial moment in the presence of the magnetic orderings with the magnetic monopole and magnetic toroidal dipole. Moreover, we specifically consider a multi-orbital model in a four-sublattice tetragonal system to demonstrate the ferro-axial moment induced by the vortex spin texture. We show that the ferro-axial moment is microscopically characterized by both the cluster-scale and atomic-scale axial-vector quantities: The former is described by the vortex of the local electric dipole and the latter is represented by the outer product of the local orbital and spin angular momenta. Moreover, we find that the atomic-spin orbit coupling and the hybridization between orbitals with different parity are key ingredients to induce the ferro-axial moment. We also apply the result to a magnetic skyrmion with a topologically-nontrivial spin texture and discuss candidate materials.

cond-mat.str-el↗