arXiv subjects

Ruo Hibino

Publications and source records attributed to Ruo Hibino.

8 recordsLinked to original sources

arXiv2026

Anomalous metallic states at magnetic interfaces in an antiferromagnetic topological insulator candidate DyPtBi with ferroquadrupolar order

Antiferromagnetic topological insulators provide a fertile platform where symmetry-breaking magnetic order is intertwined with topological electronic states. In particular, magnetic domain walls have attracted much attention, as they can be easily controlled by external fields as in general magnets, and moreover, host nontrivial electronic states distinct from those in bulks and sample surfaces. Here, we report a new antiferromagnetic topological insulator candidate DyPtBi, which hosts conductive magnetic domain walls controllable by uniaxial stress and magnetic field. We find that the resistivity exhibits abrupt increase upon the magnetic and structural phase transition. Concomitantly, the transverse ultrasonic mode shows remarkable softening of 6 %, indicating that the Dy 4f ferroquadrupolar order plays a vital role in the phase transition. Furthermore, we reveal by neutron experiments that applying compressive uniaxial stress aligns the magnetic domain state, leading to the strong resistivity enhancement of 14 % while eliminating the conductive magnetic domain walls. These findings demonstrate that DyPtBi exhibits topological electronic states entangled with multipolar degrees of freedom, providing a promising route for in situ control of topological properties.

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↗

arXiv2026

Large spontaneous Hall effect arising from collinear antiferromagnetism in Ce$_2$PtGe$_6$

The spontaneous Hall effect, corresponding to a zero-field anomalous Hall effect (AHE), is induced by symmetry breaking associated with ferromagnetism. Studies in recent years, however, have revealed that antiferromagnetic (AFM) states characterized by magnetic point groups that allow ferromagnetism can also break the relevant symmetries and induce AHE without a large net magnetization. Here, we report that the AFM system Ce$_2$PtGe$_6$ exhibits a pronounced spontaneous Hall effect. Single-crystal neutron scattering experiments demonstrate that Ce$_2$PtGe$_6$ exhibits a collinear AFM structure with a propagation vector $q=0$. The small net magnetization of $\sim 10^{-3}$ $μ_B$/Ce indicates that the observed AHE arises from symmetry breaking inherent to its AFM structure. The anomalous Hall conductivity (AHC) reaches $300$ $Ω^{-1}$cm$^{-1}$, which exceeds the intrinsic AHC of related compounds such as Ce$_2$CuGe$_6$ and Ce$_2$PdGe$_6$. This large AHC, most likely attributed to the large spin-orbit coupling of the Pt atoms, provides a platform for understanding the interplay between the Berry curvatures and localized $f$-moments with an AFM configuration.

cond-mat.str-el↗

arXiv2025

Successive Phase Transitions in the Quasi-Kagome Lattice System URhSn Studied by Resonant X-ray Scattering

Successive phase transitions in the quasi-kagome compound URhSn were investigated by resonant X-ray scattering (RXS) at the uranium $M_4$ edge. In the high-temperature phase between 16 K and 54 K, an additional RXS signal was detected superposed onto fundamental reflections in both $π$-$σ'$ and $π$-$π'$ polarization channels. Upon cooling below 16 K, reported as a ferromagnetic phase along $c$, substantial enhancements were observed again in the both polarization channels at the 300 reflection, demonstrating a simultaneous emergence of in-plane spin alongside the $c$-axis ferromagnetic components. The observed behavior can be interpreted by an antiferro-quadrupole (AFQ) order of $O_{yz}$ or $O_{zx}$ characterized by a propagation vector $q = 0$ in the intermediate phase, which then coexists with a ferromagnetic component below 16 K. The resulting ground state structure breaks the mirror symmetry perpendicular to the kagome plane, identifying the formation of a unique AFQ order with either chirality or polarity in URhSn.

cond-mat.str-el↗

arXiv2025

Elastic Softening in Synthetic Diamonds

This study reveals a previously unreported phenomenon: elastic softening of synthetic diamonds at temperatures below 1 K. We present ultrasonic measurements on single-crystalline, non-irradiated synthetic diamonds--namely, type-IIa (colorless) and type-Ib (yellow) diamonds grown by high-pressure high-temperature (HPHT) synthesis, as well as type-IIa diamond grown by chemical vapor deposition (CVD). A pronounced, divergent decrease in the elastic stiffness constant $C_{44}$ was observed in all samples down to 20 mK. We attribute this softening to electric quadrupolar degrees of freedom with irreducible representation $T_2$ in diamond. The microscopic origin of this effect, however, remains unresolved. By analogy with similar behavior observed in silicon, we suggest the presence of an as-yet-unidentified, defect-derived quantum ground state with $T_1$ or $T_2$ symmetry at ppb-level concentrations in all three diamonds studied.

cond-mat.mtrl-sci↗

arXiv2024

Magnetic Order in Honeycomb Layered U$_2$Pt$_6$Ga$_{15}$ Studied by Resonant X-ray and Neutron Scatterings

Antiferromagnetic (AF) order of U$_{2}$Pt$_{6}$Ga$_{15}$ with the ordering temperature $T_{\rm N}$ = 26 K was investigated by resonant X-ray scattering and neutron diffraction on single crystals. This compound possesses a unique crystal structure in which uranium ions form honeycomb layers and then stacks along the $c$-axis with slight offset, which gives rise to a stacking disorder. The AF order can be described with the propagation vector of $q = (1/6, 1/6, 0)$ in the hexagonal notation. The ordered magnetic moments orient perpendicular to the honeycomb layers, indicating a collinear spin structure consistent with Ising-like anisotropy. The magnetic reflections are found to be broadened along $c^*$ indicating that the stacking disorder results in anisotropic correlation lengths. The semi-quantitative analysis of neutron diffraction intensity, combined with group theory considerations based on the crystallographic symmetry, suggests a zig-zag type magnetic structure for the AF ground state, in which the AF coupling runs perpendicular to the stacking offset, characterized as $q = (1, 0, 0)_{\rm orth}$. The realization of the zig-zag magnetic structure implies the presence of frustrating intralayer exchange interactions involving both ferromagnetic (FM) first-neighbor and AF second and third-neighbor interactions in this compound.

cond-mat.str-el↗

arXiv2023

Elemental Dilution Effect on the Elastic Response due to a Quadrupolar Kondo Effect of the Non-Kramers System Y$_{1-x}$Pr$_x$Ir$_2$Zn$_{20}$

We measured the elastic constants $\left(C_{11}-C_{12}\right)/2$ and $C_{44}$ of the non-Kramers system $\rm{Y_{0.63}Pr_{0.37}Ir_{2}Zn_{20}}$ (Pr-37% system) by means of ultrasound to check how the single-site quadrupolar Kondo effect is modified by increasing the Pr concentration. The Curie-like softening of $\left(C_{11}-C_{12}\right)/2$ between 1 and 5 K of the present Pr-37% system can be reproduced by a multipolar susceptibility calculation based on the non-Kramers $Γ_3$ doublet crystalline-electric-field ground state. Further, on cooling below 0.15 K, a temperature dependence proportional to $\sqrt{T}$ was observed in $\left(C_{11}-C_{12}\right)/2$. This behavior rather corresponds to the theoretical prediction of the quadrupolar Kondo "lattice" model, unlike that of the Pr-3.4% system, which shows a logarithmic temperature dependence based on the "single-site" quadrupolar Kondo theory. In addition, we discuss the possibility to form a vibronic state by the coupling between the low-energy phonons and the electric quadrupoles of the non-Kramers doublet in the Pr-37% system, since we found a low-energy ultrasonic dispersion in the temperature region between 0.15 and 1 K.

cond-mat.str-el↗

arXiv2022

Lattice Instability of UTe$_2$ Studied by Ultrasonic Measurements

The elastic constants of an unconventional superconductor, UTe$_2$, were investigated using ultrasound. In this paper, we report the elastic response of the normal state at temperatures down to 2 K and up to 14 T for $H \parallel b$ at ambient pressure. The transverse ultrasonic mode $C_{55}$, which corresponds to the strain susceptibility of $\varepsilon_{zx}$, shows softening with decreasing temperature, whereas the $C_{44}$ and $C_{33}$ modes do not show such softening. This clear mode dependence strongly suggests that UTe$_2$ has a lattice instability for this specific symmetry.

cond-mat.supr-con↗