arXiv subjects

Shun Ito

Publications and source records attributed to Shun Ito.

5 recordsLinked to original sources

arXiv2026

Suppression of orbital ordering and emergence of a glassy magnetic state in a high-entropy spinel vanadate

High-entropy oxides provide a unique platform for exploring the interplay between configurational disorder and correlated electronic states. We report on structural, thermodynamic, and magnetic properties of the high-entropy spinel vanadate (Li$_{0.2}$Mg$_{0.2}$Mn$_{0.2}$Co$_{0.2}$Zn$_{0.2}$)V$_2$O$_4$, in which orbital-active V ions occupy the pyrochlore sublattice. X-ray diffraction measurements reveal that the cubic spinel structure is preserved at temperatures down to 5 K without any detectable symmetry lowering. Unlike conventional spinel vanadates exhibiting a symmetry-lowering structural transition driven by orbital ordering, the compound that we study exhibits a suppression of long-range orbital ordering in the high-entropy state. Magnetic susceptibility measurements show glassy magnetic freezing at temperatures below $\sim$20 K, while specific-heat measurements reveal no anomaly associated with long-range ordering down to 3 K. Frequency-dependent ac susceptibility reveals pronounced glassy dynamics. Analyses based on the Mydosh parameter, dynamic scaling law, and Vogel--Fulcher law suggest an intermediate dynamical regime between canonical spin-glass and cluster-glass behavior. Furthermore, Cole--Cole analyses reveal systematic deviations from a single Debye relaxation process, indicating the presence of heterogeneous magnetic relaxation dynamics near the freezing regime. Our results demonstrate that, in a frustrated spinel vanadate, high configurational entropy suppresses long-range orbital ordering and stabilizes a heterogeneous glassy magnetic state, highlighting the combined roles of geometrical frustration, orbital degrees of freedom, and configurational disorder in high-entropy magnets.

cond-mat.str-el↗

arXiv2026

Design and Performance of a Monolithic Plastic Scintillator Tracker with Embedded Scatterers

We propose a new scintillator-based tracker concept based on a monolithic plastic scintillator plate with embedded scatterers and wavelength-shifting fiber readout. The embedded scatterers localize scintillation light so that channels closer to the charged-particle crossing point collect more light. The particle crossing position is reconstructed from the channel-to-channel light yield distribution with a position resolution well below the readout pitch. We performed a positron beam test with prototypes to validate the reconstruction principle and to evaluate the detection efficiency and position resolution. The beam test validated the position reconstruction principle, and demonstrated a near-100% detection efficiency and a position resolution of 1.47 mm for normal incidence and 1.85 mm for an incidence angle of 45{\deg}, with a 10-mm readout pitch. In this paper, we describe the detector concept, the reconstruction method, and the results of the beam test.

physics.ins-det↗

arXiv2024

Mitigating Cognitive Biases in Multi-Criteria Crowd Assessment

Crowdsourcing is an easy, cheap, and fast way to perform large scale quality assessment; however, human judgments are often influenced by cognitive biases, which lowers their credibility. In this study, we focus on cognitive biases associated with a multi-criteria assessment in crowdsourcing; crowdworkers who rate targets with multiple different criteria simultaneously may provide biased responses due to prominence of some criteria or global impressions of the evaluation targets. To identify and mitigate such biases, we first create evaluation datasets using crowdsourcing and investigate the effect of inter-criteria cognitive biases on crowdworker responses. Then, we propose two specific model structures for Bayesian opinion aggregation models that consider inter-criteria relations. Our experiments show that incorporating our proposed structures into the aggregation model is effective to reduce the cognitive biases and help obtain more accurate aggregation results.

cs.HC↗

arXiv2016

Novel Charge Ordering in the Trimer Iridium Oxide BaIrO3

We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with face-shared Ir3O12 trimers, and have investigated the origin of the phase transition at 182 K by measuring resistivity, thermopower, magnetization and synchrotron x-ray diffraction. We propose a possible electronic model and transition mechanism, starting from a localized electron picture on the basis of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or one lattice site. The transition can be viewed as a transition from the Mott insulator phase to a kind of charge ordered insulator phase.

cond-mat.str-el↗

arXiv2014

Plasmonic generation of spin currents

Surface plasmons, free-electron collective oscillations in metallic nanostructures, provide abundant routes to manipulate light-electron interactions that can localize light energy and alter electromagnetic field distributions at subwavelength scales. The research field of plasmonics thus integrates nano-photonics with electronics. In contrast, electronics is also entering a new era of spintronics, where spin currents play a central role in driving devices. However, plasmonics and spin-current physics have so far been developed independently. Here, we demonstrate the generation of spin currents by surface plasmons. Using Au nanoparticles embedded in a Pt/BiY2Fe5O12 bilayer film, we show that, when the Au nanoparticles fulfill the surface-plasmon-resonance condition, spin currents are generated across the Pt/BiY2Fe5O12 interface. This plasmonic spin pumping results from nonequilibrium states of spins excited by surface-plasmon-induced evanescent electromagnetic fields in the BiY2Fe5O12 layer. Such plasmonic spin pumping will invigorate research on spin-current physics, and pave the way for future spin-based plasmonic devices.

cond-mat.mtrl-sci↗