arXiv subjects

Ryosuke Kurihara

Publications and source records attributed to Ryosuke Kurihara.

At least 19 recordsLinked to original sources

arXiv2026

Ultrasonic Observation of Slowing Down of Multipole Fluctuations in Sr$_2$RuO$_4$

We performed ultrasonic measurements on the unconventional superconductor Sr$_2$RuO$_4$ to investigate the dynamical properties of the electronic states near its superconducting transition temperature, $T_\mathrm{c} = 1.4$ K. We observed an increase in the in-plane transverse ultrasonic attenuation coefficient as the temperature approached $T_\mathrm{c}$. The ultrasonic attenuation exhibited a Landau-Khalatnikov-type ultrasonic frequency dependence with a typical relaxation time of approximately $10^{-10}$ s. Under an applied magnetic field of 10 T, the superconducting transition was suppressed. However, the ultrasonic attenuation coefficient exhibited an increase down to low temperatures, indicating the slowing down of fluctuations associated with multipole degrees of freedom. Based on group-theoretical considerations, we propose that the electric hexadecapole plays a crucial role in the slowing down. Furthermore, we discuss the relationship between multi-component superconducting order parameters and multipole degrees of freedom.

cond-mat.str-el↗

arXiv2026

Search for magnetoacoustic quantum oscillations in the insulating phase of YbB$_{12}$

A highly exotic phenomenon in solid-state physics is the observation of magnetic quantum oscillations in insulators. For instance, in the Kondo insulator YbB$_{12}$ various groups reported the observation of such oscillations seemingly originating from Fermi surfaces, though this contradicts the concept of an insulator having no charged quasiparticles. In this study, we searched for quantum oscillations in YbB$_{12}$ by using bulk-sensitive ultrasonic experiments in high magnetic fields up to 65 T and down to 485 mK. For that, we utilized an YbB$_{12}$ single crystal that, in previous experiments, revealed oscillations in the magnetoresistance in the insulating state. We confirmed oscillation-like behavior of the magnetoresistance as well as field-dependent oscillations in the magnetocaloric effect. However, we could not observe magnetoacoustic quantum oscillations in the insulating state, only in the field-induced metallic state. In the insulating state, we found some anomalies in our ultrasound data, the origin of which remains elusive. Our findings provide further information on the puzzling behavior of the insulating state of YbB$_{12}$.

cond-mat.str-el↗

arXiv2025

Ultrasonic observation of small Fermi surfaces in La$T$In$_5$ ($T$ = Co, Rh, Ir)

We performed high-field ultrasonic measurements on La$T$In$_5$ ($T$ = Co, Rh, Ir) to reveal the origin of the small Fermi surface that was recently observed in LaRhIn$_5$ with an oscillation frequency of 6.8 T. We observed quantum oscillations originating from this Fermi surface in LaRhIn$_5$. In addition, we revealed that LaCoIn$_5$ and LaIrIn$_5$ exhibit quantum osciilations with frequencies below 100 T, indicating hidden Fermi surfaces in these compounds. Furthermore, Co-substituted LaRhIn$_5$ exhibited quantum oscillations with a frequency of 10 T. Our results suggest that the small Fermi surface originates from bulk properties and that $3d$ electrons of the transition metal contribute to its formation.

cond-mat.str-el↗

arXiv2025

Effects of successive annealing on high-field electrical transport and the upper critical field in S-substituted FeTe

Since iron-based superconductors have been discovered, many scientists have focused on their characteristic properties, such as an unconventional mechanism and a high upper critical field. Sulphur-substituted FeTe compounds are one of the members of the iron-based superconductors; however, chemical processes, such as O$_2$ annealing, are needed to induce superconductivity because of the existence of excess iron in as-grown crystals. Thus, the removal of excess iron and the obtaining of clean sulphur-substituted FeTe can play a key role in the understanding of the superconducting properties and the application to the superconducting devices. In this study, we present the successive annealing effects on sulphur-substituted FeTe compounds to investigate the electrical transport properties under high magnetic fields. Our measurements show that successive annealing processes improve the electrical transport properties in the superconducting states under magnetic fields. The removal of excess iron acting as magnetic impurities is indicated by the improvement of the upper critical field and its analysis.

cond-mat.supr-con↗

arXiv2025

Removal of excess iron by annealing processes and emergence of bulk superconductivity in sulfur-substituted FeTe

There are several strategies to discover new superconductors. Growing new materials and applying high pressures can be the classic ways since superconductivity was found. Also, chemical processing, such as annealing, is another way to induce superconductivity in a non-superconducting material. Here, we show chemical processing effects in the non-superconducting material, sulfur-substituted FeTe. It has been known that superconductivity in S-substituted FeTe is induced by O$_2$ annealing. We revealed that hydrochloric acid etching and vacuum annealing for O$_2$-annealed samples made the quality of superconductivity higher by several physical property measurements. Furthermore, we visualized the superconducting regions by a magneto-optical imaging technique, indicating that the superconductivity in the processed sample was bulk. In this sample, we confirmed that the concentration of excess iron was reduced compared to that in the as-grown state. These results provide an important route to bulk superconductivity in S-substituted FeTe and its related iron-based compounds.

cond-mat.supr-con↗

arXiv2024

Emergence of ferroelectric topological insulator as verified by quantum Hall effect of surface states in (Sn,Pb,In)Te films

Emergent phenomena arising from nontrivial band structures based on topology and symmetry have been attracting keen interest in contemporary condensed-matter physics. Materials such as SnTe and PbTe are one such example, which demonstrate a topological phase transition while showing ferroelectric instability derived from their rock-salt structure. The ferroelectricity can lift the valley degeneracy, enabling the emergence of the Z2 topological insulator phase, although its observation in transport phenomena remains elusive. Here, we report magnetotransport properties of ferroelectric (Sn,Pb)Te thin films with finely-controlled Fermi levels via In doping. We identified the ferroelectric topological insulator phase from the observations of the quantum Hall states with filling factors of $\nu$ = 1, 2 and 3 with both spin- and valley-degeneracy lifting. The electronic states are two-dimensional, indicating the ferroelectricity-induced topological surface states with a single Dirac cone. The finding of the new topological state with ferroelectricity will further expand the field of topological physics and advance the development of functional properties, such as topological nonlinear photonics and nonreciprocal transport with memory effect.

cond-mat.mtrl-sci↗

arXiv2024

Quantum liquid states of spin solitons in a ferroelectric spin-Peierls state

In this study, we performed high-magnetic-field magnetization, dielectric, and ultrasound measurements on an organic salt showing a ferroelectric spin-Peierls (FSP) state, which is in close proximity to a quantum critical point. In contrast to the sparsely distributed gas-like spin solitons typically observed in conventional spin-Peierls (SP) states, the FSP state exhibits dense liquid-like spin solitons resulting from strong quantum fluctuations, even at low fields. Nevertheless, akin to conventional SP systems, a magnetic-field-induced transition is observed in the FSP state. In conventional high-field SP states, an emergent wave vector results in the formation of a spin-soliton lattice. However, in the present high-field FSP state, the strong quantum fluctuations preclude the formation of such a soliton lattice, causing the dense solitons to remain in a quantum-mechanically melted state. This observation implies the realization of a quantum liquid--liquid transition of topological particles carrying spin and charge in a ferroelectric insulator.

cond-mat.str-el↗

arXiv2023

Edge and bulk states in Weyl-orbit quantum Hall effect as studied by Corbino measurements

We investigate edge and bulk states in Weyl-orbit based quantum Hall effect by measuring a Corbino-type device fabricated from a topological Dirac semimetal (Cd1-xZnx)3As2 film. Clear quantum Hall plateaus are observed when measuring one-sided terminals of the Corbino-type device. This indicates that edge states of the Weyl-orbit quantum Hall effect form closed trajectories consisting of Fermi arcs and chiral zero modes independently on inner and outer sides. On the other hand, the bulk resistance does not diverge at fields where the quantum Hall plateau appears, suggesting that the Weyl orbits in the bulk region are not completely localized when applying electric current through the bulk region.

cond-mat.mes-hall↗

arXiv2023

Carrier filtering effect for enhanced thermopower in a body-centered tetragonal ruthenate

Charged carriers in solids diffuse from hot to cold sides under temperature gradient to induce the thermoelectric voltage. Carrier filtering effect, which only passes either electrons or holes for the conduction process, is an efficient method to enhance such voltage, although it is challenging to experimentally realize it especially in conventional metals with weak energy dependence of the density of states near the Fermi level. Here we measure the in-plane and out-of-plane thermopower of the layered perovskite Sr$_2$RuO$_4$ single crystals above room temperature, and find that the out-of-plane thermopower is largely enhanced with increasing temperature, while the in-plane one seems to remain a temperature-independent constant value which is expected from the Heikes formula. The observed large out-of-plane thermopower may originate from the recently proposed intriguing hole filtering effect in the body-centered tetragonal system, in which the carrier hopping through the centered atom is essential. Thus, the present carrier filtering effect may be a universal property to be applicable in various materials belonging to such crystal system.

cond-mat.str-el↗

arXiv2022

High-Field Ultrasonic Study of CeIrIn$_5$

We performed ultrasonic and temperature measurements under pulsed magnetic fields on CeIrIn$_5$ to investigate whether or not the origin of metamagnetic transition and field-induced Lifshitz transition was described by the anisotropic electronic ordering with crystal symmetry breaking. We observed elastic anomalies with the negative magnetocaloric effects around the field-induced Lifshitz transition and the metamagnetic transition. On the other hand, the elastic anomalies appeared both in the transverse elastic constants $(C_{11} - C_{12})/2$ and $C_{66}$ in CeIrIn$_5$ while $(C_{11} - C_{12})/2$ showed significant elastic anomaly at the crystal symmetry breaking fields in CeRhIn$_5$. These results indicate that the anisotropic electronic ordering with crystal symmetry breaking is absent in high-magnetic fields in CeIrIn$_{5}$.

cond-mat.str-el↗

arXiv2022

SmI3: 4f5 honeycomb magnet with spin-orbital entangled {\Gamma}7 Kramers doublet

We report magnetic properties of a 4f-honeycomb iodide SmI3 made up of edge-shared network of SmI6 octahedra. High temperature magnetic susceptibility indicates {\Gamma}7 Kramers doublet ground state of Sm3+ (4f5) ions stabilized by the spin-orbit coupling and octahedral crystal electric field, which interact with Sm-I-Sm bond angle nearly 90 degree. Magnetization measurements down to 0.1 K detected antiferromagnetic correlations and an anomaly in the magnetization curve before saturation without a sign of long-range order. Relevance between SmI3 and the antiferromagnetic Kitaev material proposed in the 4f-electron system is discussed.

cond-mat.str-el↗

arXiv2022

Highly anisotropic geometrical Hall effect via f-d exchange fields in doped pyrochlore molybdates

When a conduction electron couples with a non-coplanar localized magnetic moment, the realspace Berry curvature is exerted to cause the geometrical Hall effect, which is not simply proportional to the magnetization. So far, it has been identified in the case mostly where the non-coplanar magnetic order is present on the sublattice of conduction electrons. Here, we demonstrate that the geometrical Hall effect shows up even without long-range magnetic order of conduction electrons, as induced by non-coplanar exchange fields from the localized magnetic moments, in hole-doped phyrochlore molybdates. We find that the geometrical Hall effect is markedly anisotropic with respect to the applied magnetic field direction, which is in good accordance with the field-dependent magnitude and sign change of the real-space scalar spin chirality of local Tb moments. These results may facilitate the understanding of emergent electromagnetic responses induced by the Kondo-like coupling between conduction electrons and local spins in a broad material class.

cond-mat.mtrl-sci↗

arXiv2022

Ferroelectric transition of a chiral molecular crystal BINOL2DMSO

We report dielectric, thermodynamical, acoustic, and optical properties of a chiral molecular crystal, 1,1'-bi-2-naphthol 2-dimethylsulfoxide (BINOL2DMSO). We find two successive phase transitions at Tc1=190 K and Tc2=125 K. The first transition at Tc1 is characterized by an order-disorder transition of the guest molecules DMSO along with ferroelectricity. At the second transition of Tc2, the crystal structure deforms from tetragonal to monoclinic, leading to domain formation. Low-temperature x-ray diffraction suggests that the space group changes from P4_12_12 (P4_32_12) to P4_1 (P4_3) at Tc1, and down to P112_1 at Tc2.

cond-mat.mtrl-sci↗

arXiv2022

Elastic Soft Mode and Electric Quadrupole Response in Excitonic Insulator Candidate (Ta$_{0.952}$V$_{0.048}$)$_2$NiSe$_5$: Contribution of Electron-Phonon Interaction

We performed ultrasonic measurements on (Ta$_{0.952}$V$_{0.048}$)$_2$NiSe$_5$ to investigate the contribution of acoustic phonons at the zone center to structural and possible excitonic transitions. The transverse elastic constant $C_{55}$ with irreducible representation $B_\mathrm{2g}$ exhibits softening over 90\% above a transition temperature of $T_\mathrm{s} = 280$ K, indicating the soft mode of corresponding TA phonons. Our analysis based on the quadrupole response indicates that the electron-phonon interaction contributes to the excitonic transition in addition to the hybridization between the conduction and valence bands if the excitonic transition is realized.

cond-mat.str-el↗

arXiv2022

Extremely high upper critical field in BiCh$_2$-based (Ch: S and Se) layered superconductor LaO$_{0.5}$F$_{0.5}$BiS$_{2-x}$Se$_x$ ($x$ = 0.22 and 0.69)

Centrosymmetric compounds with local inversion symmetry breaking have tremendously interesting and intriguing physical properties. In this study, we focus on a BiCh$_2$-based (Ch: S, Se) layered superconductor, as a system with local inversion asymmetry, because spin polarisation based on the Rashba-Dresselhaus-type spin-orbit coupling has been observed in centrosymmetric BiCh$_2$-based LaOBiS$_2$ systems, while the BiCh$_2$ layer lacks local inversion symmetry. Herein, we report the existence of extremely high in-plane upper critical fields in the BiCh$_2$-based system LaO$_{0.5}$F$_{0.5}$BiS$_{2-x}$Se$_x$ ($x$ = 0.22 and 0.69). The superconducting states are not completely suppressed by the applied magnetic fields with strengths up to 55 T. Thus, we consider that the in-plane upper critical field is enhanced by the local inversion symmetry breaking and its layered structure. Our study will open a new pathway for the discovery of superconductors that exhibit a high upper critical field by focusing on the local inversion symmetry breaking.

cond-mat.supr-con↗

arXiv2021

Tunable spin-valley coupling in layered polar Dirac metals

In non-centrosymmetric metals, spin-orbit coupling (SOC) induces momentum-dependent spin polarization at the Fermi surfaces. This is exemplified by the valley-contrasting spin polarization in monolayer transition metal dichalcogenides (TMDCs) with in-plane inversion asymmetry. However, the valley configuration of massive Dirac fermions in TMDCs is fixed by the graphene-like structure, which limits the variety of spin-valley coupling. Here, we show that the layered polar metal BaMn$X_2$ ($X =$Bi, Sb) hosts tunable spin-valley-coupled Dirac fermions, which originate from the distorted $X$ square net with in-plane lattice polarization. We found that in spite of the larger SOC, BaMnBi$_2$ has approximately one-tenth the lattice distortion of BaMnSb$_2$, from which a different configuration of spin-polarized Dirac valleys is theoretically predicted. This was experimentally observed as a clear difference in the Shubnikov-de Haas oscillation at high fields between the two materials. The chemically tunable spin-valley coupling in BaMn$X_2$ makes it a promising material for various spin-valleytronic devices.

cond-mat.str-el↗

arXiv2021

Quantum transport of topological spin solitonsin a one-dimensional organic ferroelectric

We report the dielectric, magnetic, and ultrasonic properties of a one-dimensional organic salt TTF-QBr$_3$I. These indicate that TTF-QBr$_3$I shows a ferroelectric spin-Peierls (FSP) state in a quantum critical regime. In the FSP state, coupling of charge, spin, and lattice leads to emergent excitation of spin solitons as topological defects. Amazingly, the solitons are highly mobile even at low temperatures, although they are normally stationary because of pinning. Our results suggest that strong quantum fluctuations enhanced near a quantum critical point enable soliton motion governed by athermal relaxation. This indicates the realization of quantum topological transport at ambient pressure.

cond-mat.str-el↗

arXiv2021

Quantum transport observed in films of magnetic topological semimetal EuSb$_2$

We report fabrication of EuSb$_2$ single-crystalline films and investigation of their quantum transport. First-principles calculations demonstrate that EuSb$_2$ is a magnetic topological nodal-line semimetal protected by nonsymmorphic symmetry. Observed Shubnikov-de Haas oscillations with multiple frequency components exhibit small effective masses and two-dimensional field-angle dependence even in a 250 nm thick film, further suggesting possible contributions of surface states. This finding of the high-mobility magnetic topological semimetal will trigger further investigation of exotic quantum transport phenomena by controlling magnetic order in topological semimetal films.

cond-mat.mtrl-sci↗