Publications by authors named "Yasutaka Imanaka"

Since the discovery of the Verwey transition in magnetite, transition metal compounds with pyrochlore structures have been intensively studied as a platform for realizing remarkable electronic phase transitions. We report on a phase transition that preserves the cubic symmetry of the β-pyrochlore oxide CsWO, where each of W 5d electrons are confined in regular-triangle W trimers. This trimer formation represents the self-organization of 5d electrons, which can be resolved into a charge order satisfying the Anderson condition in a nontrivial way, orbital order caused by the distortion of WO octahedra, and the formation of a spin-singlet pair in a regular-triangle trimer.

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Article Synopsis
  • The study reports the observation of fractional quantum Hall (FQH) plateaus in a bilayer electron gas system, specifically in wide InGaAs wells.
  • FQH states are confirmed at higher temperatures (around 1.6 K) under certain conditions, including an imbalance in electron density and unique resistance behavior during the transition between bilayer and monolayer states.
  • The diversity of observed fractional plateaus varies by sample due to the influence of impurities or defects, indicating that these plateaus serve as a "fingerprint" unique to each sample.
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Stimulated by strong demand for thermal expansion control from advanced modern industries, various giant negative thermal expansion (NTE) materials have been developed during the last decade. Nevertheless, most such materials exhibit anisotropic thermal expansion in the crystal lattice. Therefore, strains and cracks induced during repeated thermal cycling degrade their performance as thermal-expansion compensators.

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We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) conditions and investigate its structural, magnetic, dielectric, and ferroelectric properties. We find that PbMn7O12 exhibits rich physical properties from interplay among charge, orbital, and spin degrees of freedom and rich structural properties. PbMn7O12 crystallizes in space group R3̅ near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure in space group Im3̅; the Im3̅-to-R3̅ transition is associated with charge ordering.

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TlMO(3) perovskites (M(3+) = transition metals) are exceptional members of trivalent perovskite families because of the strong covalency of Tl(3+)-O bonds. Here we report on the synthesis, crystal structure and properties of TlCrO(3) investigated by Mössbauer spectroscopy, specific heat, dc/ac magnetization and dielectric measurements. TlCrO(3) perovskite is prepared under high pressure (6 GPa) and high temperature (1500 K) conditions.

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Cyclotron resonance (CR) measurements for the Fe-based superconductor KFe(2)As(2) are performed. One signal for CR is observed, and is attributed to the two-dimensional α Fermi surface at the Γ point. We found a large discrepancy in the effective masses of CR [(3.

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Near-field scanning optical microscope (NSOM or SNOM) is a form of scanning probe microscope (SPM), which is used to observe the optical properties of a sample surface with a nanometer-scale spatial resolution. Since the near-field light strongly interacts with the sample surface, or with nanometer-scale objects on the substrate's surface, NSOM is advantageous to excite only the vicinity of a sample surface. From the view point of surface chemical analysis, a discussion about the light energy concentration within a nanometer-scale region, and an estimation of its efficiency are indispensable for accurate measurements of the optical properties in a nanometer-scale region.

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