arXiv subjects

Kazumasa Hattori

Publications and source records attributed to Kazumasa Hattori.

At least 19 recordsLinked to original sources

arXiv2026

Chiral Valence-Bond Solid and Chiral Triplons

We propose a chiral valence-bond solid (VBS) state that spontaneously breaks inversion and mirror symmetries. It is characterized by a finite electric toroidal (ET) monopole, whose sign distinguishes the two enantiomorphic states. Using a spin-lattice model with Dzyaloshinskii-Moriya interactions, we show that the chiral VBS produces spin-split triplon bands with enantiomer-dependent spin textures governed by its ET monopole. Under a temperature gradient, these spin textures generate a net spin response whose sign is tied to the handedness of the VBS. More importantly, we show that the imaginary off-diagonal components of the dynamical spin structure factor change sign between the two enantiomers, providing a direct neutron-scattering probe of the selected handedness. These results establish a route to spontaneous chirality in a valence-bond system and to its direct detection through magnetic excitations.

cond-mat.str-el↗

arXiv2026

Order parameter scaling of chirality in structural phase transitions

Chirality, defined by the absence of mirror and inversion symmetries, has attracted considerable attention owing to its unique physical phenomena, including cross-correlated responses such as current-induced magnetization (CIM) and chiral phonons. Recently, it has been established that chirality is characterized by electric toroidal (ET) multipoles: the ET monopole $G_0$ in cubic systems and the ET quadrupole $G_u$ in noncubic systems. In this paper, we investigate achiral-to-chiral (AtC) structural phase transitions driven by atomic displacements and construct $G_{0,u}$ as explicit functions of the displacement order parameter $η$ based on a group-theoretical approach. We show that the leading-order dependence of $G_{0,u}(η)$ is determined by the symmetry of the parent structure and the character of the displacive mode, providing a symmetry-based classification of AtC transitions beyond a binary distinction between achiral and chiral phases. We also demonstrate that $G_{0,u}(η)$ is directly reflected in observable quantities such as CIM and chiral phonon splitting (CPS), both of which scale consistently with $G_{0,u}(η)$. We further clarify the microscopic mechanism by which AtC transitions give rise to chiral phonons and CPS through the coupling between $G_{0,u}(η)$ and phonon degrees of freedom.

cond-mat.str-el↗

arXiv2026

L-point quadrupole order under magnetic field in cubic PrIr$_2$Zn$_{20}$

We study quadrupole orders in heavy-fermion compound PrIr$_2$Zn$_{20}$ under magnetic fields on the basis of the Landau theory. Assuming $E_g$ electric quadrupolar orders in the cubic symmetry with the ordering wavenumber at the L points in the face-centered cubic lattice Brillouin zone as observed experimentally, we construct a Landau free energy and analyze the resulting free energy. We find that the unidentified high-temperature ordered phase under the magnetic field ${\bf H} \parallel [001]$ reported earlier arises from the rotation of the quadrupole moments of f electrons on the Pr site. We also discuss the phase diagram for other magnetic-field directions and possible double-${\bf q}$ quadrupolar orders in this system.

cond-mat.str-el↗

arXiv2026

Successive single-q and double-q orders in an anisotropic XY model on the diamond structure: a model for quadrupole ordering in PrIr$_2$Zn$_{20}$

Quadrupole ordering with the ordering wavevector at the L points in PrIr$_2$Zn$_{20}$ under magnetic fields is analyzed using classical Monte Carlo simulations based on an effective $Γ_3$ quadrupole model on the diamond structure. We demonstrate that competition between the magnetic field and quadrupole anisotropy leads to a rich phase diagram for magnetic fields applied parallel to [001], which includes switching between a single-q state and a double-q state. We also show that a symmetry-allowed biquadratic intersite interaction, corresponding to a hexadecapole interaction, is crucial for reproducing the weak-field topology observed in experiments.

cond-mat.str-el↗

arXiv2026

Collinear Magnetic Structure in the Diamond Network Magnet EuTi$_2$Al$_{20}$

The magnetic structure of EuTi$_2$Al$_{20}$, in which magnetic Eu$^{2+}$ ions form a diamond network, was investigated using neutron and resonant X-ray diffraction on powder and single-crystal samples. The propagation vector was determined to be $\textbf{\textit{q}}_{\rm m}=(1,0,0)$~r.l.u. from these diffraction measurements. All possible magnetic structures in the space group $Fd\bar{3}m$ with this propagation vector were examined using the irreducible representation method and magnetic space group analysis. This magnetic structure was identified as a collinear antiferromagnetic structure with the magnetic space group $P_Inna$ (\#52.320) or $P_Inn2$ (\#34.164) under zero magnetic field. In these magnetic structure, frustration arises from competing magnetic interactions on the diamond network. These findings provide a concrete experimental reference for assessing the role of competing interactions in diamond-network magnets and motivate further studies of interaction-driven quantum states.

cond-mat.str-el↗

arXiv2026

Flexocurrent-induced magnetization: Strain gradient-induced magnetization in time-reversal symmetric systems

Symmetry constraints determine which physical responses are allowed in a given system. Magnetization induced by strain fields, such as in piezomagnetic and flexomagnetic effects, has typically been considered in materials that break time-reversal symmetry. Here, we propose that nonuniform strain can induce magnetization even in nonmagnetic metals and semiconductors that preserve time-reversal symmetry. This mechanism differs from the conventional flexomagnetic effect: the strain gradient acts as a driving force on the electrons, generating magnetization in a manner closely analogous to current-induced magnetization. Treating the strain field as an external field, we derive a general expression for the magnetization induced by a strain gradient and demonstrate that this response is symmetry-allowed even in time-reversal symmetric systems. We apply our formulation to nonmagnetic systems that lack spatial inversion symmetry while preserving time-reversal symmetry, using a decorated square lattice, monolayer MoS$_2$, and monolayer Janus MoSSe as representative examples. We find a finite magnetization response to strain gradients, which is consistent with symmetry arguments, supporting the validity of our theoretical framework. These results offer a pathway for controlling magnetization in nonmagnetic materials using strain fields.

cond-mat.mtrl-sci↗

arXiv2026

Purely Electronic Chirality without Structural Chirality

We introduce the concept of purely electronic chirality (PEC), which arises in the absence of structural chirality. In condensed matter physics and chemistry, chirality has conventionally been understood as a mirror-image asymmetry in crystal or molecular structures. We demonstrate that certain electronic orders exhibit chirality-related properties without atomic displacement. Specifically, we investigate quadrupole orders to realize such purely electronic chirality with handedness that can be tuned by magnetic fields. As a representative example, we analyze a model featuring $120^circ$ antiferro quadrupole orders on a distorted kagomé lattice, predicting various chirality-related responses in the nonmagnetic ordered phase of URhSn. Furthermore, as a phonon analog, chiral phonons can emerge in achiral crystals through coupling with the PEC order. Our results provide a distinct origin of chirality and a fundamental basis for exploring the interplay between electronic and structural chirality.

cond-mat.str-el↗

arXiv2025

Probing magnetic-field-induced multipolar ordering through field-angle-resolved magnetostriction and thermal expansion in PrIr$_2$Zn$_{20}$

We performed field-angle-resolved magnetostriction and thermal-expansion measurements on PrIr$_2$Zn$_{20}$, a cubic non-Kramers compound exhibiting antiferroquadrupolar order below $T_{\rm Q}=0.125$ K. Thermal expansion exhibits two qualitatively different anomalies under magnetic fields applied along the $[001]$ direction, providing experimental support for the existence of an intermediate A phase previously reported. Furthermore, comparison between the experimental results and theoretical modeling indicates a strong anisotropic coupling of the $O_{20}$ quadrupolar moment, which plays a key role in stabilizing the A phase. These findings demonstrate that multipolar states in non-Kramers systems can be effectively tuned by magnetic-field orientation, providing insights into the anisotropic nature of quadrupolar interactions.

cond-mat.str-el↗

arXiv2025

Kondo-Peierls transition with nonsymmorphic zone boundary gap formation

We study nonsymmorphic space group symmetry breakings in correlated electron systems. Under nonsymmorphic symmetry, it is well known that there are degeneracies in the electronic Bloch states at the Brillouin zone boundaries. When the system undergoes a phase transition into an ordered phase with breaking the nonsymmorphic symmetry, the degeneracy is lifted. This happens even when the order parameter is uniform. We point out that this general feature leads to various {\it uniform} Peierls transition in nonsymmorphic systems. In particular, we show that such mechanism of the Peierls gap formation can be realized accompanying with uniform anisotropic Kondo singlet formations. This explains the hidden electric order observed in CeCoSi.

cond-mat.str-el↗

arXiv2025

Spin-flip Scattering at a Chiral Interface of Helical Chains

We investigate spin-flip scattering processes of electrons when they pass a chiral interface, which is the boundary between right- and left-handed one-dimensional chain. We construct a minimal $p$-orbital model consisting of the right- and left-handed one-dimensional threefold helical chains connected at $z=0$ with the nearest neighbor hopping and the spin-orbit coupling. The dynamics of spin-polarized wave packet passing through the interface, the Green's functions, and electronic states near the interface are analyzed numerically. We find that the microscopic structure of the interface is important and this strongly affects the local electronic orbital state. This in addition to the spin-orbit coupling determines whether the spin flip occurs or not at the chiral interface and suggests a possible spin transport control by the orbital configuration at the chiral interface.

cond-mat.mes-hall↗

arXiv2025

Order parameter fluctuation effects on current-induced magnetization

We investigate the impact of order parameter fluctuations on magnetoelectric effects in metallic systems using classical Monte Carlo simulations. We focus on a a chiral quadrupole order in a distorted kagome lattice in a model incorporating conduction electrons and classical orbital moments. The ordered orbital moments break mirror symmetry and couple with the conduction electrons, leading to a current-induced magnetization driven by the quadrupole order. Our findings reveal that order parameter fluctuations significantly affect the current-induced magnetization, strongly suppressing the response over a broad temperature range below the transition temperature. Additionally, we analyze the influence of Fermi surface properties and associated matrix elements on this phenomenon. Our results highlight the crucial role of fluctuation effects, demonstrating a qualitatively distinct temperature dependence of the current-induced magnetization compared to that of the order parameter itself.

cond-mat.str-el↗

arXiv2023

Quadrupole partial orders and triple-$q$ states on the face-centered cubic lattice

We study $Γ_3$ quadrupole orders in a face-centered cubic lattice. The $Γ_3$ quadrupole moments under cubic symmetry possess a unique cubic invariant in their free energy in the uniform ($q=0$) sector and the triple-q sector for the X points $q=(2π,0,0),(0,2π,0)$, and $(0,0,2π)$. Competition between this cubic anisotropy and anisotropic quadrupole-quadrupole interactions causes a drastic impact on the phase diagram both in the ground state and at finite temperatures. We show details about the model construction and its properties, the phase diagram, and the mechanism of the various triple-$q$ quadrupole orders reported in our preceding letter [J. Phys. Soc. Jpn. 90, 43701 (2021), arXiv:2102.06346]. By using a mean-field approach, we analyze a quadrupole exchange model that consists of a crystalline-electric field scheme with the ground-state $Γ_3$ non-Kramers doublet and the excited singlet $Γ_1$ state. We find various triple-$q$ orders in the four-sublattice mean-field approximation. A few partial orders of quadrupoles are stabilized in a wide range of parameter space at a higher transition temperature than single-$q$ orders. With lowering the temperature, these partial orders undergo phase transitions into further symmetry broken phases in which nonvanishing quadrupole moments emerge at previously disordered sites. The obtained phases in the mean-field approximation are investigated by a phenomenological Landau theory, which clearly shows that the cubic invariant plays an important role for stabilizing the triple-$q$ states. We also discuss its implications for recent experiments in a few f- and d-electron compounds.

cond-mat.str-el↗

arXiv2023

Electronic origin of ferroic quadrupole moment under antiferroic quadrupole orders and finite magnetic moment in $J_{\rm eff}=3/2$ systems

We study the electronic origin of parasitic ferroic quadrupole moments in antiferroic quadrupole orders by extending a model studied in G. Chen et al., Phys. Rev. B 82, 174440 (2010) with the effective angular momentum $J_{\rm eff}=3/2$ quartet ground states. Taking into account the first crystalline-electric-field (CEF) excited doublet, cubic anisotropy in the quadrupole moments emerges, which leads to the induced ferroic quadrupole moments in the antiferro quadrupolar phases. The hybridization with the CEF excited quartet states also causes finite magnetic moments compatible to the observed size of the effective moment in typical $J_{\rm eff}=3/2$ systems, as opposed to the naive expectation of vanishing moments in the $J_{\rm eff}=3/2$ systems. These results suggest the importance of the corrections arising from the high-energy CEF excited states in the $J_{\rm eff}=3/2$ systems.

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

Triple-$\mathcal{Q}$ partial magnetic orders induced by quadrupolar interactions: Triforce order scenario for UNi$_4$B

We theoretically investigate possible symmetry-broken states in ${\rm UNi_4B}$, constructing a localized pseudo triplet crystalline-electric field model. For a long time, its low-temperature symmetry-broken phase in ${\rm UNi_4B}$ has been considered to be a magnetic toroidal order forming atomic-scale vortices lattice with disordered sites at each center of the vortices. However, recent observation of current-induced magnetizations offers a reinvestigation about the validity of this order parameter because of the contradiction in their anisotropy. Our model takes into account the quadrupole degrees of freedom, whose importance is recently evidenced by the sound-velocity softening. We find that the quadrupole moments play an important role in determining the magnetic structure in the ordered states. For a wide range of parameter space, we obtain two triple-$\mathcal{Q}$ magnetic orders in our 36-site mean-field analysis: toroidal order and another one with the same number of disordered sites as in the toroidal order. We name the latter ``triforce'' order after its magnetic structure. Importantly, the triforce order possesses exactly the same spin structure factor as the toroidal order does, while the phase factors in the superposition of the triple-$\mathcal{Q}$ structure are different. We show that the triforce order is consistent with the observed current-induced magnetization when the realistic crystal structure of ${\rm UNi_4B}$ is taken into account. We compare the predictions of the triforce order with the experimental data available at present in detail and also discuss possible applications of the present mechanism of triple-$\mathcal{Q}$ orders to anisotropic correlated systems.

cond-mat.str-el↗

arXiv2021

Triple-$q$ quadrupole-octupole order scenario for PrV$_2$Al$_{20}$

We propose novel triple-${\bm q}$ multipole orders as possible candidates for the two distinct low-temperature symmetry broken phases in quadrupolar system PrV$_2$Al$_{20}$. An analysis of the experiment under [111] magnetic fields indicates that the {\it ferro} octupole moments in the lower temperature phase arise from the {\it antiferro} octupole interactions. We demonstrate that the triple-${\bm q}$ multipole orders can solve this seemingly inconsistent issue. Anisotropies of quadrupole moments stabilize a triple-${\bm q}$ order, which further leads to the second transition to a coexisting phase with triple-${\bm q}$ octupole moments. The cubic invariant of quadrupole moments formed by the triple-${\bm q}$ components and the characteristic couplings with the octupole moments in their free energy play important roles. We analyze a multipolar exchange model by mean-field approximation and discuss the temperature and magnetic field phase diagrams. Many of the microscopic results, such as the number of phases and the magnitudes of critical fields in the phase diagrams, are qualitatively consistent with the experiments in PrV$_2$Al$_{20}$.

cond-mat.str-el↗

arXiv2021

Quadrupole Orders on the fcc Lattice

We theoretically study electric quadrupole orders in f-electron systems on the fcc lattice. Qudrupole degrees of freedom $O_{20}$ and $O_{22}$ originate in the non-Kramers doublet ground state $Γ_3$ of ion with $f^2$ electron configuration. For discussing quadrupole orders, we use a minimal model with isotropic ($J$) and anisotropic ($K$) nearest-neighbor interactions, and determine the phase diagram using a four-site mean-field approximation at zero and finite temperatures. Quadrupoles couple the $Γ_3$ doublet to the singlet excited state $Γ_1$, and its effects on canting antiferro orders are examined in detail. We found that this coupling leads to a rich phase diagram including two- and four-sublattice antiferro phases, and that two phases show a partial order of quadrupoles at finite temperatures.

cond-mat.str-el↗

arXiv2020

Field-Orientation Effect on Ferro-Quadrupole Order in PrTi2Al20

Ferro-quadrupole (FQ) order in the non-Kramers $Γ_3$ doublet system PrTi$_2$Al$_{20}$ has been investigated via angle-resolved measurements of the specific heat, rotational magnetocaloric effect, and entropy, under a rotating magnetic field within the $(1\bar{1}0)$ plane. The FQ transition occurring at 2 K is robust when the magnetic field $B$ is applied precisely along the $[111]$ direction. By contrast, the magnetic field of larger than 1 T tilted away from the $[111]$ direction sensitively changes the FQ transition to a crossover. The energy gap between the ground and first-excited states in the FQ order increases remarkably with the magnetic field in $B \parallel [001]$, but hardly depends on the magnetic-field strength, at least up to 5 T, in the field orientation between the $[111]$ and $[110]$ axes. These features can be reproduced by using a phenomenological model for FQ order assuming an anisotropic field-dependent interaction between quadrupoles, which has been recently proposed to explain the field-induced first-order phase transition in PrTi$_2$Al$_{20}$. The present study demonstrates the great potential of the field-angle-resolved measurements for evaluating possible scenarios for multipole orders.

cond-mat.str-el↗