arXiv subjects

R. Arita

Publications and source records attributed to R. Arita.

At least 19 recordsLinked to original sources

arXiv2026

Large magneto-optical Kerr effect induced by collinear antiferromagnetic order

In modern technology, the optical readout of magnetic information is conventionally achieved by the magneto-optical Kerr effect, i.e., the polarization rotation of reflected light. The Kerr rotation is sensitive to time-reversal symmetry breaking and generally proportional to magnetization, enabling optical readout of the up and down spin states in ferromagnets. By contrast, antiferromagnets with a collinear antiparallel spin arrangement have long been considered inactive to such magneto-optical responses, because of Tt-symmetry (time-reversal T followed by translation t symmetry) and lack of macroscopic magnetization. Here, we report the observation of giant magneto-optical Kerr effect in a room-temperature antiferromagnetic insulator alpha-Fe2O3. In this compound, the up-down and down-up spin states induce the opposite sign of spontaneous Kerr effect, whose Kerr rotation angle turned out to be exceptionally large (~ 80 mdeg, comparable to typical ferromagnets). Our first-principles calculations successfully reproduce both the absolute magnitude and spectral shape of the Kerr rotation and ellipticity with remarkable accuracy, which unambiguously proves that it originates from a Tt-symmetry-broken collinear antiferromagnetic order, rather than magnetization. This compound hosts temperature-dependent transition between easy-plane and easy-axis antiferromagnetic states, and their contrasting behaviors are also investigated in detail. The present results demonstrate that even a simple collinear antiferromagnetic order can induce a giant magneto-optical Kerr effect, and highlight Tt-symmetry-broken antiferromagnets as a promising material platform for highly sensitive optical detection of up-down and down-up spin states.

cond-mat.str-el↗

arXiv2025

Mass enhancement and metal-nonmetal transition driven by d-f hybridization in perovskites La1-xPrxCuO3

We report the large electron-mass enhancement and the metal to nonmetal transition upon the Pr doping in perovskite-type La1-xPrxCuO3. With increasing the Pr content x around 0.6, the LaCuO3-type three-dimensional structure with trivalent Cu ions changes to the quasi-one-dimensional structure with nearly divalent Cu ions, which accompanies significant changes in the electronic properties. Based on the resistivity, optical conductivity, specific heat measurements and the first-principles calculations, we discuss the formation of a nearly localized nonmetallic state stabilized by the hybridization between Cu 3d, O 2p, and Pr 4f orbitals in the quasi-one-dimensional lattice. The present perovskite-type cuprates offer a unique opportunity to explore novel quantum phases of correlated electrons in low-dimensional lattice, where the spin/charge/orbital degrees of freedom of A- and B-site ions are entangled.

cond-mat.str-el↗

arXiv2024

Generation of Weyl points and a nodal line by magnetization reorientation in Co$_3$Sn$_2$S$_2$

Topological magnets exhibit fascinating properties like topologically protected surface states or anomalous transport phenomena. While these properties can be significantly altered by manipulating the magnetic state, the experimental verification of such predictions remains challenging. Here, we demonstrate the efficient magnetic field control of the Weyl semimetallic state of the collinear ferromagnet Co$_3$Sn$_2$S$_2$ by magneto-optical spectroscopy. We resolve a redshift of the nodal loop resonance as the magnetization is rotated into the kagome plane by the magnetic field. Our material-specific theory, capturing the observed field-induced spectral reconstruction, shows the creation of 26 Weyl points for one in-plane magnetization direction and predicts the emergence of a gapless nodal loop for the orthogonal in-plane magnetization orientation. These findings demonstrate that while topological band structures are generally considered robust, breaking underlying crystal symmetries with external fields provides an efficient way to manipulate them, even in collinear magnets. This approach opens exciting avenues to control band topology also in materials with more complex magnetic structures and even to study the interplay of real- and momentum-space topological states, e.g. in skyrmion-lattice systems.

cond-mat.mtrl-sci↗

arXiv2024

Optical anisotropy of the kagome magnet FeSn: Dominant role of excitations between kagome and Sn layers

Antiferromagnetic FeSn is considered to be a close realization of the ideal two-dimensional (2D) kagome lattice, hosting Dirac cones, van Hove singularities, and flat bands, as it comprises Fe$_3$Sn kagome layers well separated by Sn buffer layers. We observe a pronounced optical anisotropy, with the low-energy optical conductivity being surprisingly higher perpendicular to the kagome planes than along the layers. This finding contradicts the prevalent picture of dominantly 2D electronic structure for FeSn. Our material-specific theory reproduces the measured conductivity spectra remarkarbly well. A site-specific decomposition of the optical response to individual excitation channels shows that the optical conductivity for polarizations both parallel and perpendicular to the kagome plane is dominated by interlayer transitions between kagome layers and adjacent Sn-based layers. Moreover, the matrix elements corresponding to these transitions are highly anisotropic, leading to larger out-of-plane conductivity. Our results evidence the crucial role of interstitial layers in charge dynamics even in seemingly 2D systems.

cond-mat.mtrl-sci↗

arXiv2024

Gapped nodal planes drive a large topological Nernst effect in a chiral lattice antiferromagnet

The electronic structure of compensated antiferromagnets (CAF) has drawn attention for its ability to create large responses, reminiscent of ferromagnets and suitable for data storage and readout, despite (nearly) net-zero spontaneous magnetization. Many of the striking experimental signatures predicted for CAF, such as giant thermoelectric Nernst effects, are enhanced when two or more electronic bands are nearly degenerate in vicinity of the Fermi energy. Here, we use thermoelectric and electric transport experiments to study the electronic structure of the layered, chiral metal CoNb3S6 in its all-in-all-out CAF ground state and report near-degeneracies of electron bands at the upper and lower boundaries of the first Brillouin zone. Considering non-symmorphic spin-space group symmetries in the non-relativistic approximation for the ordered phase, these near-degeneracies are approximately protected by a lattice translation combined with spin rotation, and are vestiges of nodal planes enforced by a screw axis symmetry in the paramagnetic state. Hot spots of emergent, or fictitious, magnetic fields are formed at the slightly gapped nodal plane, generating the spontaneous Hall and Nernst effects in this CAF. Taking into account more than six hundred Wannier orbitals, our model quantitatively reproduces the observed spontaneous Nernst effect, emphasizes the role of proximate symmetries in the emergent responses of CAF, and demonstrates the promise of ab-initio search for functional responses in a wide class of materials with reconstructed unit cells due to spin or charge order.

cond-mat.mtrl-sci↗

arXiv2023

180$^\circ$-twisted bilayer ReSe$_2$ as an artificial noncentrosymmetric semiconductor

We have fabricated a 180$^\circ$-twisted bilayer ReSe$_2$ by stacking two centrosymmetric monolayer ReSe$_2$ flakes in opposite directions, which is expected to lose spatial inversion symmetry. By the second harmonic generation and angle-resolved photoemission spectroscopy, we successfully observed spatial inversion symmetry breaking and emergent band dispersions. The band calculation shows the finite lifting of spin degeneracy (~50 meV) distinct from natural monolayer and bilayer ReSe$_2$. Our results demonstrate that the spin-momentum locked state, which leads to spintronic functions and Berry-curvature-related phenomena, can be realized even with the stacking of centrosymmetric monolayers.

cond-mat.mes-hall↗

arXiv2023

Intertwined Charge and Spin Density Waves in a Topological Kagome Material

Using neutrons and x-rays we show the topological kagome antiferromagnet Mn$_3$Sn for $T<285$~K forms a homogeneous spin and charge ordered state comprising a longitudinally polarized spin density wave (SDW) with wavevector $\textbf{k}_{\beta}=k_\beta {\bf \hat{c}}$, a helical modulated version of the room temperature anti-chiral magnetic order with $\textbf{k}_{\chi}=k_\chi{\bf \hat{c}}$, and charge density waves with wave vectors $2\textbf{k}_\beta, 2\textbf{k}_\chi$, and $\textbf{k}_\beta+\textbf{k}_\chi$. Though $\textbf{k}_{\chi}$ and $\textbf{k}_\beta$ coincide for $200~{\rm K}<T<230$~K, they exhibit distinct continuous $T-$dependencies before locking to commensurate values of $\textbf{k}_{\beta} = \frac{1}{12}\textbf{c}^{*}$ and $\textbf{k}_{\chi} = \frac{5}{48}\textbf{c}^{*}$ at low$-T$. Density functional theory indicates this complex modulated state may be associated with the nesting of Fermi surfaces from correlated flat kagome bands, which host Weyl nodes that are annihilated as it forms.

cond-mat.str-el↗

arXiv2023

Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials

In ferromagnets, electric current generally induces transverse Hall voltage in proportion to magnetization (anomalous Hall effect), and it is frequently used for electrical readout of the up and down spin states. While these properties are usually not expected in antiferromagnets, recent theoretical studies predicted that non-coplanar antiferromagnetic order with finite scalar spin chirality (i.e. solid angle spanned by neighboring spins) can often induce large spontaneous Hall effect even without net magnetization or external magnetic field. This phenomenon, i.e. spontaneous topological Hall effect, can potentially be used for the efficient electrical readout of the antiferromagnetic states, but its experimental verification has long been elusive due to the lack of appropriate materials hosting such exotic magnetism. Here, we report the discovery of all-in-all-out type non-coplanar antiferromagnetic order in triangular lattice compounds CoTa3S6 and CoNb3S6, by performing the detailed magnetic structure analysis based on polarized neutron scattering experiments as well as systematic first-principles calculations. These compounds are reported to host unconventionally large spontaneous Hall effect despite their vanishingly small net magnetization, and our analysis revealed that it can be well explained in terms of topological Hall effect, which originates from the fictitious magnetic field associated with scalar spin chirality in non-coplanar antiferromagnetic orders. The present results indicate that the scalar spin chirality mechanism can offer a promising route to realize giant spontaneous Hall response even in compensated antiferromagnets, and highlight intercalated van der Waals magnets as an unique quasi-two-dimensional material platform to enable various nontrivial manner of electrical reading and possible writing of non-coplanar antiferromagnetic domains.

cond-mat.mtrl-sci↗

arXiv2023

Nodal line resonance generating the giant anomalous Hall effect of Co$_3$Sn$_2$S$_2$

Giant anomalous Hall effect (AHE) and magneto-optical activity can emerge in magnets with topologically non-trivial degeneracies. However, identifying the specific band structure features like Weyl points, nodal lines or planes which generate the anomalous response is a challenging issue. Since the low-energy interband transitions can govern the static AHE, we addressed this question in the prototypical magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ also hosting nodal lines by broadband polarized reflectivity and magneto-optical Kerr effect spectroscopy with a focus on the far-infrared range. In the linear dichroism spectrum we observe a strong resonance at 40\,meV, which also shows up in the optical Hall conductivity spectrum and primarily determines the static AHE, thus, confirms its intrinsic origin. Our material-specific theory reproduces the experimental data remarkably well and shows that strongly tilted nodal line segments around the Fermi energy generate the resonance. While the Weyl points only give vanishing contributions, these segments of the nodal lines gapped by the spin-orbit coupling dominate the low-energy optical response.

cond-mat.str-el↗

arXiv2022

Quantum oscillations in a centrosymmetric skyrmion-hosting magnet GdRu2Si2

We have performed magnetic torque and resistivity measurements on a centrosymmetric skyrmion-host GdRu2Si2, in which the dominant magnetic interaction leading to skyrmion formation is under debate. We observe both the de Haas-van Alphen and Shubnikov-de Haas oscillations in the forced ferromagnetic phase. The angular dependence of the quantum oscillation frequencies can be reproduced by the ab-initio calculation. The de Haas-van Alphen oscillation is also observed in the double-Q phase with a different frequency to that in the forced ferromagnetic phase, indicating a Fermi surface reconstruction due to the coupling between localized spins and conduction electrons. Based on these experimental findings, the magnetic interactions in this system are discussed.

cond-mat.str-el↗

arXiv2021

Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor

In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the electronic structure near the Fermi level is characterized by fermions with angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$) states become allowed. Prime candidates for such exotic states are half-Heusler superconductors, which exhibit unconventional superconducting properties, but their pairing nature remains unsettled. Here we show that the superconductivity in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by the admixture of isotropic even-parity singlet and anisotropic odd-parity septet pairing, whose ratio can be tuned by electron irradiation. From magnetotransport and penetration depth measurements, we find that carrier concentrations and impurity scattering both increase with irradiation, resulting in a nonmonotonic change of the superconducting gap structure. Our findings shed new light on our fundamental understanding of unconventional superconducting states in topological materials.

cond-mat.supr-con↗

arXiv2021

Field-induced multiple metal-insulator crossovers of correlated Dirac electrons of perovskite CaIrO$_3$

The interplay between electron correlation and topology of relativistic electrons may lead to a new stage of the research on quantum materials and emergent functions. The emergence of various collective electronic orderings/liquids, which are tunable by external stimuli, is a remarkable feature of correlated electron systems, but has rarely been realized in the topological semimetals with high-mobility relativistic electrons. Here, we report that the correlated Dirac electrons with the Mott criticality in perovskite CaIrO$_3$ show unconventional field-induced successive metal-insulator-metal crossovers in the quantum limit accompanying a giant magnetoresistance (MR) with MR ratio of 3,500 % (18 T and 1.4 K). The analysis shows that the insulating state originates from the collective electronic ordering such as charge/spin density wave promoted by electron correlation, whereas it turns into the quasi-one-dimensional metal at higher fields due to the field-induced reduction of chemical potential, highlighting the highly field-sensitive character of correlated Dirac electrons.

cond-mat.str-el↗

arXiv2021

Multipole polaron in the devil's staircase of CeSb

Rare-earth intermetallic compounds exhibit rich phenomena induced by the interplay between localized $f$ orbitals and conduction electrons. However, since the energy scale of the crystal-electric-field splitting is only a few millielectronvolts, the nature of the mobile electrons accompanied by collective crystal-electric-field excitations has not been unveiled. Here, we examine the low-energy electronic structures of CeSb through the anomalous magnetostructural transitions below the N$\'{e}$el temperature, $\sim$17 K, termed the 'devil's staircase', using laser angle-resolved photoemission, Raman and neutron scattering spectroscopies. We report another type of electron-boson coupling between mobile electrons and quadrupole crystal-electric-field excitations of the 4$f$ orbitals, which renormalizes the Sb 5$p$ band prominently, yielding a kink at a very low energy ($\sim$7 meV). This coupling strength is strong and exhibits anomalous step-like enhancement during the devil's staircase transition, unveiling a new type of quasiparticle, named the 'multipole polaron', comprising a mobile electron dressed with a cloud of the quadrupole crystal-electric-field polarization.

cond-mat.mtrl-sci↗

arXiv2021

Direct observation of the layer-number-dependent electronic structure in few-layer WTe2

When a crystal becomes thinner and thinner to the atomic level, peculiar phenomena discretely depending on its layer-numbers (n) start to appear. The symmetry and wave functions strongly reflect the layer-numbers and stacking order, which brings us a potential of realizing new properties and functions that are unexpected in either bulk or simple monolayer. Multilayer WTe2 is one such example exhibiting unique ferroelectricity and non-linear transport properties related to the antiphase stacking and Berry-curvature dipole. Here we investigate the electronic band dispersions of multilayer WTe2 (2-5 layers), by performing laser-based micro-focused angle-resolved photoelectron spectroscopy on exfoliated-flakes that are strictly sorted by n and encapsulated by graphene. We clearly observed the insulator-semimetal transition occurring between 2- and 3-layers, as well as the 30-70 meV spin-splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our result fully demonstrates the possibility of the large energy-scale band and spin manipulation through the finite n stacking procedure.

cond-mat.mtrl-sci↗

arXiv2020

High-pressure synthesis of Ba$_2$RhO$_4$, a rhodate analogue of the layered perovskite Sr-ruthenate

A new layered perovskite-type oxide Ba$_2$RhO$_4$ was synthesized by a high-pressure technique with the support of convex-hull calculations. The crystal and electronic structure were studied by both experimental and computational tools. Structural refinements for powder x-ray diffraction data showed that Ba$_2$RhO$_4$ crystallizes in a K$_2$NiF$_4$-type structure, isostructural to Sr$_2$RuO$_4$ and Ba$_2$IrO$_4$. Magnetic, resistivity, and specific heat measurements for polycrystalline samples of Ba$_2$RhO$_4$ indicate that the system can be characterized as a correlated metal. Despite the close similarity to its Sr$_2$RuO$_4$ counterpart in the electronic specific heat coefficient and the Wilson ratio, Ba$_2$RhO$_4$ shows no signature of superconductivity down to 0.16 K. Whereas the Fermi surface topology has reminiscent pieces of Sr$_2$RuO$_4$, an electron-like e$_g$-($d_{x^2-y^2}$) band descends below the Fermi level, making of this compound unique also as a metallic counterpart of the spin-orbit-coupled Mott insulator Ba$_2$IrO$_4$.

cond-mat.str-el↗

arXiv2020

Topological Kagome magnet Co3Sn2S2 thin flakes with high electron mobility and large anomalous Hall effect

Magnetic Weyl semimetals attract considerable interest not only for their topological quantum phenomena but also as an emerging materials class for realizing quantum anomalous Hall effect in the two-dimensional limit. A shandite compound Co3Sn2S2 with layered Kagome-lattices is one such material, where vigorous efforts have been devoted to synthesize the two-dimensional crystal. Here we report a synthesis of Co3Sn2S2 thin flakes with a thickness of 250 nm by chemical vapor transport method. We find that this facile bottom-up approach allows the formation of large-sized Co3Sn2S2 thin flakes of high-quality, where we identify the largest electron mobility (~2,600 cm2V-1s-1) among magnetic topological semimetals, as well as the large anomalous Hall conductivity (~1,400 Ω-1cm-1) and anomalous Hall angle (~32 %) arising from the Berry curvature. Our study provides a viable platform for studying high-quality thin flakes of magnetic Weyl semimetal and stimulate further research on unexplored topological phenomena in the two-dimensional limit.

cond-mat.mtrl-sci↗

arXiv2020

Devil's staircase transition of the electronic structures in CeSb

Solids with competing interactions often undergo complex phase transitions with a variety of long-periodic modulations. Among such transition, devil's staircase is the most complex phenomenon, and for it, CeSb is the most famous material, where a number of the distinct phases with long-periodic magnetostructures sequentially appear below the Neel temperature. An evolution of the low-energy electronic structure going through the devil's staircase is of special interest, which has, however, been elusive so far despite the 40-years of intense researches. Here we use bulk-sensitive angle-resolved photoemission spectroscopy and reveal the devil's staircase transition of the electronic structures. The magnetic reconstruction dramatically alters the band dispersions at each transition. We moreover find that the well-defined band picture largely collapses around the Fermi energy under the long-periodic modulation of the transitional phase, while it recovers at the transition into the lowest-temperature ground state. Our data provide the first direct evidence for a significant reorganization of the electronic structures and spectral functions occurring during the devil's staircase.

cond-mat.mtrl-sci↗

arXiv2019

Multipole expansion for magnetic structures: A generation scheme for symmetry-adapted orthonormal basis set in crystallographic point group

We propose a systematic method to generate a complete orthonormal basis set of multipole expansion for magnetic structures in arbitrary crystal structure. The key idea is the introduction of a virtual atomic cluster of a target crystal, on which we can clearly define the magnetic configurations corresponding to symmetry-adapted multipole moments. The magnetic configurations are then mapped onto the crystal so as to preserve the magnetic point group of the multipole moments, leading to the magnetic structures classified according to the irreducible representations of crystallographic point group. We apply the present scheme to pyrhochlore and hexagonal ABO3 crystal structures, and demonstrate that the multipole expansion is useful to investigate the macroscopic responses of antiferromagnets.

physics.comp-ph↗