"published_papers" "Title(English)","Title(Japanese)","Author(s)(English)","Author(s)(Japanese)","Journal name(English)","Journal name(Japanese)","Volume","Number","First page","Last page","Date of publication","Peer reviewed/Not peer reviewed","Invited/Not invited","Publishing type","Language","ISSN","DOI","URL","Description(English)","Description(Japanese)" "Phase transitions and slow spin dynamics of slightly inverted A-site spinel CoAl2−x Ga x O4","Phase transitions and slow spin dynamics of slightly inverted A-site spinel CoAl2−x Ga x O4","T Naka, J Valenta, T Nakane, S Ishii, M Nakayama, H Mamiya, K Takehana, N Tsujii, Y Imanaka, Y Matsushita, H Abe, T Uchikoshi, H Yusa","T Naka, J Valenta, T Nakane, S Ishii, M Nakayama, H Mamiya, K Takehana, N Tsujii, Y Imanaka, Y Matsushita, H Abe, T Uchikoshi, H Yusa","Journal of Physics: Condensed Matter","Journal of Physics: Condensed Matter","36","12","125801","","2024-03-27","TRUE","","scientific_journal","eng","","10.1088/1361-648x/ad12fc","","We report the properties of an A-site spinel magnet, CoAl2−xGaxO4, and analyze its anomalous, low-temperature magnetic behavior, which is derived from inherent, magnetically frustrated interactions. Rietveld analysis of the x-ray diffraction profile for CoAl2−xGaxO4 revealed that the metallic ions were randomly distributed in the tetrahedral (A-) and octahedral (B-) sites in the cubic spinel structure. The inversion parameter eta could be controlled by varying the gallium (Ga) composition in the range 0.055 ≤ eta ≤ 0.664. The composition-induced Néel-to-spin-glass (NSG) transition occurred between 0.05 ≤ eta ≤ 0.08 and was verified by measurements of DC-AC susceptibilities chi and thermoremanent magnetization (TRM) below the Néel transition temperature TN. The relaxation rate and derivative with respect to temperature of TRM increased at both TN and the spin glass (SG) transition temperature TSG. The TRM decayed rapidly above and below these transitions. TRM was highly sensitive to macroscopic magnetic transitions that occurred in both the Néel and SG phases of CoAl2−xGaxO4. In the vicinity of the NSG boundary, there was a maximum of the TRM relaxation rate at Tmax < TN. With increasing inversion eta(x), the anomaly at Tmax merged with that of the Néel transition at a tricritical point (etatc, Ttc) = (0.08, 4.0 K), where the paramagnetic, Néel, and SG states met. We successfully extracted the relaxation time tau and other characteristic parameters from the TRM isothermal temporal evolution based on the Weron function derived for a purely stochastic process. To distinguish the magnetic states, we compared our results with previously studied inversion-free A-site spinel, CoRh2O4, and CoGa2O4 cluster glass. ","" "Fabrication of AlGaN/GaN heterostructures on halide vapor phase epitaxy AlN/SiC templates for high electron mobility transistor application","Fabrication of AlGaN/GaN heterostructures on halide vapor phase epitaxy AlN/SiC templates for high electron mobility transistor application","Masatomo Sumiya, Osamu Goto, Yuki Takahara, Yasutaka Imanaka, Liwen Sang, Noboru Fukuhara, Taichiro Konno, Fumimasa Horikiri, Takeshi Kimura, Akira Uedono, Hajime Fujikura","Masatomo Sumiya, Osamu Goto, Yuki Takahara, Yasutaka Imanaka, Liwen Sang, Noboru Fukuhara, Taichiro Konno, Fumimasa Horikiri, Takeshi Kimura, Akira Uedono, Hajime Fujikura","Japanese Journal of Applied Physics","Japanese Journal of Applied Physics","62","8","085501","","2023-08-01","TRUE","","scientific_journal","eng","","10.35848/1347-4065/ace671","","GaN films were grown on HVPE-AlN/SiC templates by metalorganic chemical vapor deposition (MOCVD) without annealing a reactor to eliminate memory effect. Step-terrace structure and smooth surface were obtained for GaN film with a thickness of ~200 nm. Subsequently, AlGaN/GaN heterostructures for the application of high electron mobility transistors (HEMTs) with thin GaN channel were fabricated with no C or Fe-doped GaN buffer layer. The interface quality at AlGaN/GaN heterostructure was good enough for two-dimensional electron gas (2DEG) to exhibit Shubnikov-de Haas oscillation in the magnetic field at 1.8 K. The GaN HEMTs with a thin channel on the AlN/SiC templates exhibited both pinch-off character and conventional properties. In view of both the shorter epitaxial-growth time and higher thermal conduction, HVPE-AlN/SiC templates are applicable to the fabrication of GaN HEMTs by MOCVD.","" "Electrical-field-induced insulator-to-metal transition in samarium monosulfides","Electrical-field-induced insulator-to-metal transition in samarium monosulfides","K. Kishida, J. Shibutani, T. Hatano, Y. Yokoyama, N. Katayama, Y. Okamoto, Y. Nakamura, H. Kishida, H. S. Suzuki, K. Takehana, Y. Imanaka, K. Takenaka","K. Kishida, J. Shibutani, T. Hatano, Y. Yokoyama, N. Katayama, Y. Okamoto, Y. Nakamura, H. Kishida, H. S. Suzuki, K. Takehana, Y. Imanaka, K. Takenaka","Applied Physics Letters","Applied Physics Letters","121","12","121901","","2022-09-19","TRUE","","scientific_journal","eng","","10.1063/5.0108716","","Electrical-field-induced insulator-to-metal (I-to-M) transition of samarium monosulfides was investigated systematically. Experiment results demonstrate that Sm0.9Ca0.1S undergoes the I-to-M transition when in a small electric field of 250V/cm at liquid-nitrogen temperatures. However, simultaneous measurement of I–V characteristics and strain did not detect the electrical-field-induced strain expected from the large volume contraction originating from the valence transition of Sm. Mid-infrared to visible region reflectivity spectroscopy in the field- induced transition revealed no spectral change other than the temperature change attributable to Joule heat. This lack of change contrasts to the large-scale spectrum changes, such as a sharp rise in reflectivity, which appear in the metallic phase induced by pressure or element sub- stitution. The detailed analysis of the field-induced strain suggests that filamentary metallic paths are formed during the breakdown process, just as they are for strongly correlated insulators.","" "Relief of spin frustration through magnetic anisotropy in the quasi-one-dimensional S=12 antiferromagnet Na2CuSO4Cl2","Relief of spin frustration through magnetic anisotropy in the quasi-one-dimensional S=12 antiferromagnet Na2CuSO4Cl2","M. Fujihala, Y. Sakuma, S. Mitsuda, A. Nakao, K. Munakata, R. A. Mole, S. Yano, D. H. Yu, K. Takehana, Y. Imanaka, M. Akaki, S. Okubo, H. Ohta","M. Fujihala, Y. Sakuma, S. Mitsuda, A. Nakao, K. Munakata, R. A. Mole, S. Yano, D. H. Yu, K. Takehana, Y. Imanaka, M. Akaki, S. Okubo, H. Ohta","Physical Review B","Physical Review B","105","14","","","2022-04-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.105.144410","","We report the magnetic structure and anisotropy of the quasi-one-dimensional S = 21 antiferromagnet Na2CuSO4Cl2 obtained by single-crystal neutron scattering, electron spin resonance (ESR), and magnetization measurements, following an earlier study of its dynamics [M. Fujihala et al., Phys. Rev. B 101, 024410 (2020)]. A Néel-type spin structure is formed within the chain of this compound, where the spins point along the b axis, and ESR data indicate an antisymmetric exchange with a uniform Dzyaloshinskii-Moriya (DM) vector pointing along the b axis. The anisotropy g factor and magnetic structure are strong indicators of magnetic anisotropy originating from a symmetric anisotropic exchange interaction and/or a magnetic dipole interaction. These results suggest that these terms of the anisotropic spin Hamiltonian counteract the effect of the DM interaction and stabilize the Néel-type structure in Na2CuSO4Cl2.","" "Growth of AlxGa1-xN/InyGa1-yN hetero structure on AlN/sapphire templates exhibiting Shubnikov-de Haas oscillation","Growth of AlxGa1-xN/InyGa1-yN hetero structure on AlN/sapphire templates exhibiting Shubnikov-de Haas oscillation","Masatomo Sumiya, Yuki Takahara, Amira Alghamdi, Yoshiko Nakayama, Fumihiko Uesugi, Yoshitomo Harada, Akira Uedono, Yasutaka Imanaka","Masatomo Sumiya, Yuki Takahara, Amira Alghamdi, Yoshiko Nakayama, Fumihiko Uesugi, Yoshitomo Harada, Akira Uedono, Yasutaka Imanaka","Journal of Crystal Growth","Journal of Crystal Growth","574","","126324","","2021-11-01","TRUE","","scientific_journal","eng","","10.1016/j.jcrysgro.2021.126324","","We fabricated successfully heterostructures of AlGaN/GaN and AlGaN/InGaN/GaN on AlN template/c-sapphire exhibiting the Shubnikov-de Haas (SdH) oscillation in the magnetic field at lower temperatures. In AlxGa1-xN/GaN system, the carrier density of two-dimensional electron gas (2DEG) was controlled from 4.0×1012 to 9.0×1012 cm-2, which was consistent with the theoretical simulation, with increase of Al composition in AlGaN barrier layer. In AlGaN/InGaN/GaN system, the surface morphology and alloy disorder on the InGaN were properly defined. The effective mass of 2DEG at the Al0.22Ga0.78N/In0.04Ga0.96N interface was estimated to be 0.24m0 from the temperature dependence of SdH oscillation amplitude. Although the effective mass was comparable to that of AlGaN/GaN heterostructure, the mobility of 2DEG at the InGaN was drastically degraded in spite of the slight amount of indium incorporation. This reduction was attributed to larger scattering probably due to the interface roughness of InGaN layer caused by the step meandering and/or the potential fluctuation caused by random incorporation of indium atoms.","" "Regular-triangle trimer and charge order preserving the Anderson condition in the pyrochlore structure of CsW2O6","Regular-triangle trimer and charge order preserving the Anderson condition in the pyrochlore structure of CsW2O6","Yoshihiko Okamoto, Haruki Amano, Naoyuki Katayama, Hiroshi Sawa, Kenta Niki, Rikuto Mitoka, Hisatomo Harima, Takumi Hasegawa, Norio Ogita, Yu Tanaka, Masashi Takigawa, Yasunori Yokoyama, Kanji Takehana, Yasutaka Imanaka, Yuto Nakamura, Hideo Kishida, Koshi Takenaka","Yoshihiko Okamoto, Haruki Amano, Naoyuki Katayama, Hiroshi Sawa, Kenta Niki, Rikuto Mitoka, Hisatomo Harima, Takumi Hasegawa, Norio Ogita, Yu Tanaka, Masashi Takigawa, Yasunori Yokoyama, Kanji Takehana, Yasutaka Imanaka, Yuto Nakamura, Hideo Kishida, Koshi Takenaka","Nature Communications","Nature Communications","11","1","","","2020-12-01","TRUE","","scientific_journal","eng","","10.1038/s41467-020-16873-7","","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 CsW2O6, where each of W 5d electrons are confined in regular-triangle W3 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 WO6 octahedra, and the formation of a spin-singlet pair in a regular-triangle trimer. An electronic instability due to the unusual three-dimensional nesting of Fermi surfaces and the strong correlations of the 5d electrons characteristic of the pyrochlore oxides are both likely to play important roles in this charge-orbital-spin coupled phenomenon.","" "Growth of AlGaN/InGaN/GaN Heterostructure on AlN Template/Sapphire","Growth of AlGaN/InGaN/GaN Heterostructure on AlN Template/Sapphire","Masatomo Sumiya, Dickson Kindole, Kiyotaka Fukuda, Shuhei Yashiro, Kanji Takehana, Tohru Honda, Yasutaka Imanaka","Masatomo Sumiya, Dickson Kindole, Kiyotaka Fukuda, Shuhei Yashiro, Kanji Takehana, Tohru Honda, Yasutaka Imanaka","physica status solidi (b)","physica status solidi (b)","257","4","1900524","","2020-04-01","TRUE","","scientific_journal","eng","","10.1002/pssb.201900524","","GaN films are grown directly on AlN templates/sapphire substrates without using low-temperature (LT) buffer layers by metalorganic chemical vapor deposition. AlN templates are complimentarily deformed at the initial growth of GaN, adjusting the a-lattice constant and tilting crystal orientation slightly. Compared with the film on sapphire substrates using an LT buffer layer, the GaN on the AlN template forms a smoother surface and has better crystalline quality after a shorter growth time at a lower temperature. Higher quality InGaN films on the GaN/AlN template are subsequently grown to optimize the thickness exhibiting the minimum Urbach energy which is evaluated by photothermal deflection spectroscopy. A high-quality AlGaN/ InGaN heterostructure is fabricated in which the Shubnikov–de Haas oscillation can be clearly observed from the electron gas of the InGaN channel at the interface.","" "Giant isotropic negative thermal expansion in Y-doped samarium monosulfides by intra-atomic charge transfer","Giant isotropic negative thermal expansion in Y-doped samarium monosulfides by intra-atomic charge transfer","Koshi Takenaka, Daigo Asai, Ryoichi Kaizu, Yosuke Mizuno, Yasunori Yokoyama, Yoshihiko Okamoto, Naoyuki Katayama, Hiroyuki S. Suzuki, Yasutaka Imanaka","Koshi Takenaka, Daigo Asai, Ryoichi Kaizu, Yosuke Mizuno, Yasunori Yokoyama, Yoshihiko Okamoto, Naoyuki Katayama, Hiroyuki S. Suzuki, Yasutaka Imanaka","Scientific Reports","Scientific Reports","9","1","","","2019-12-01","TRUE","","scientific_journal","eng","","10.1038/s41598-018-36568-w","","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. Here we achieved giant isotropic NTE with volume change exceeding 3%, up to 4.1%, via control of the electronic configuration in Sm atoms of SmS, (4f)6 or (4f)5(5d)1, by partial replacement of Sm with Y. Contrary to NTE originating from cooperative phenomena such as magnetism, the present NTE attributable to the intra-atomic phenomenon avoids the size effect of NTE and therefore provides us with fine-grained thermal-expansion compensators, which are strongly desired to control thermal expansion of microregions such as underfill of a three-dimensional integrated circuit. Volume control of lanthanide monosulfides via tuning of the 4f electronic configuration presents avenues for novel mechanical functions of a material, such as a volume-change driven actuator by an electrical field, which has a different drive principle from those of conventional strain-driven actuators such as piezostrictive or magnetostrictive materials.","" "Fractional quantum Hall effects in In0.75Ga0.25As bilayer electron systems observed as “Finger print”","Fractional quantum Hall effects in In0.75Ga0.25As bilayer electron systems observed as “Finger print”","Syoji Yamada, Akira Fujimoto, Siro Hidaka, Masashi Akabori, Yasutaka Imanaka, Kanji Takehana","Syoji Yamada, Akira Fujimoto, Siro Hidaka, Masashi Akabori, Yasutaka Imanaka, Kanji Takehana","Scientific Reports","Scientific Reports","9","1","","","2019-12-01","TRUE","","scientific_journal","eng","","10.1038/s41598-019-43290-8","","Observations of fractional quantum Hall (FQH) plateaus are reported in bilayer electron gas system in wide (> 80 nm) In0.75Ga0.25As wells. Several q / p (p = 5, 3, and 2, q > 5) QH states are confirmed at high temperatures (~ 1.6 K) when the critical conditions including an electron density imbalance as well as a dynamical resistance behavior at the bilayer-monolayer transition are properly satisfied. The former leads to a quantum limit in either of the layers and the latter might bring a meta-stable nature into FQH phenomena. Such a behavior occurs as a probability process associating with impurities or defects in the wells, they inevitably reflect the local structural landscapes of each sample. This is verified by the new finding that the kinds of fractional plateaus (what set of fractional filling factors) appeared are different depending on the samples, that is, they are the “finger print” in each sample.","" "Effects of Y substitution on the electronic structure and charge dynamics of SmS","Effects of Y substitution on the electronic structure and charge dynamics of SmS","Y. Yokoyama, H. Hasegawa, Y. Mizuno, D. Asai, Y. Okamoto, H. S. Suzuki, K. Takehana, Y. Imanaka, K. Takenaka","Y. Yokoyama, H. Hasegawa, Y. Mizuno, D. Asai, Y. Okamoto, H. S. Suzuki, K. Takehana, Y. Imanaka, K. Takenaka","Physical Review B","Physical Review B","100","24","","","2019-12-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.100.245143","","Evolution of the electronic state by Y doping was explored by optical conductivity covering a wide energy and compositional region deduced from systematic reflectivity measurements of Sm1−xYxS single crystals. Although electrons doped onto the 5d band by Y dopants immediately realize a metallic state, the charge dynamics do not obey a simple Drude response and the spectral intensity is condensed in the mid-infrared region. Contrary to the pressure-induced case, a metallic phase appears in a certain compositional region before reaching the valence transition. The Fermi level is shifted upwards by electron doping. Therefore, the 5d band must overlap with the weakly dispersive 4f band more deeply than in the pressure-induced case to reach the valence transition, which can explain the stability of the divalent phase up to higher temperatures in the doped system than in the pressure-induced case. The present optical study provides us with a strategy that sulfur deficiency might increase operating temperature of negative thermal expansion in this system.","" "Nonlinear piezomagnetoelectric effect in CuFeO2","Nonlinear piezomagnetoelectric effect in CuFeO2","H. Tamatsukuri, S. Mitsuda, T. Shimizu, M. Fujihala, H. Yokota, K. Takehana, Y. Imanaka, A. Nakao, K. Munakata","H. Tamatsukuri, S. Mitsuda, T. Shimizu, M. Fujihala, H. Yokota, K. Takehana, Y. Imanaka, A. Nakao, K. Munakata","Physical Review B","Physical Review B","100","20","","","2019-11-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.100.201105","","We investigate novel phenomena correlated with multiple degrees of freedom in a geometrically frustrated magnet, CuFeO2, by applying uniaxial pressure p and magnetic field H. Ferroelectric polarization is induced by a combination of p and H only in a sinusoidally amplitude-modulated magnetic structure phase, in which the sinusoidal magnetic ordering does not break the inversion symmetry. The crystal structure and magnetic structure in this phase seem to be unchanged, even by the application of p and H within the present neutron diffraction experiments. These results indicate that this phenomenon differs from conventional spin-driven ferroelectricity as observed in a H-induced helical magnetic phase of CuFeO2. We propose that the induction of ferroelectric polarization by the combined application of p and H in CuFeO2 can be regarded as a nonlinear piezomagnetoelectric effect.","" "Valence fluctuations and giant isotropic negative thermal expansion in Sm1–xRxS (R = Y, La, Ce, Pr, Nd)","Valence fluctuations and giant isotropic negative thermal expansion in Sm1–xRxS (R = Y, La, Ce, Pr, Nd)","D. Asai, Y. Mizuno, H. Hasegawa, Y. Yokoyama, Y. Okamoto, N. Katayama, H. S. Suzuki, Y. Imanaka, K. Takenaka","D. Asai, Y. Mizuno, H. Hasegawa, Y. Yokoyama, Y. Okamoto, N. Katayama, H. S. Suzuki, Y. Imanaka, K. Takenaka","Applied Physics Letters","Applied Physics Letters","114","14","141902","","2019-04-08","TRUE","","scientific_journal","eng","","10.1063/1.5090546","","The valence fluctuations of Sm in SmS are known to induce possible large isotropic negative thermal expansion (NTE), but difficulty in crystal growth prevents establishment of the NTE function. For this study, we prepared Ce-doped and Nd-doped SmS polycrystalline samples using a simpler method with much lower reaction temperature than the existing method. Typically, Sm0.80Ce0.20S exhibits giant NTE with total volume change of 2.6% in the wide temperature range from 330 K to 100 K, the lowest covered here. Achievement of giant NTE in a low-cost polycrystalline form paves the way for practical applications of this class of sulfides as a thermal- expansion compensator.","" "Terahertz Cyclotron Resonance in AlGaN/GaN Heterostructures","Terahertz Cyclotron Resonance in AlGaN/GaN Heterostructures","Dickson Kindole, Yasutaka Imanaka, Kanji Takehana, Liwen Sang, Masatomo Sumiya","Dickson Kindole, Yasutaka Imanaka, Kanji Takehana, Liwen Sang, Masatomo Sumiya","Journal of the Korean Physical Society","Journal of the Korean Physical Society","74","2","159","163","2019-01-01","TRUE","","scientific_journal","eng","","10.3938/jkps.74.159","","Cyclotron resonance (CR) in AlGaN/GaN two-dimensional electron system is investigated under high magnetic fields up to 15T in order to study the magnetic field dependence of the electron effective mass. Nonlinear dependence of the CR energy against the magnetic field is observed, indicating that the effective mass becomes heavier with increasing the magnetic field. This is partially due to the contribution from the resonant polaron effect because GaN have the larger electron-longitudinal-optical (LO) phonon interaction among III-V compounds. The magnetic field dependence of the CR energy is explained well with the Fr ̈ohlich polaron theory in the magnetic field.","" "Magnetic field tunable dielectric dispersion in successive field-induced magnetic phases of the geometrically frustrated magnet CuFeO2 up to 28 T","Magnetic field tunable dielectric dispersion in successive field-induced magnetic phases of the geometrically frustrated magnet CuFeO2 up to 28 T","H. Tamatsukuri, S. Mitsuda, K. Hiroura, T. Nakajima, M. Fujihala, M. Yamano, Y. Toshioka, C. Kaneko, K. Takehana, Y. Imanaka, N. Terada, H. Kitazawa","H. Tamatsukuri, S. Mitsuda, K. Hiroura, T. Nakajima, M. Fujihala, M. Yamano, Y. Toshioka, C. Kaneko, K. Takehana, Y. Imanaka, N. Terada, H. Kitazawa","Physical Review B","Physical Review B","97","21","","","2018-06-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.97.214407","","We find magnetic-field-dependent dielectric dispersions specific to successive field-induced magnetic phases of a geometrically frustrated magnet CuFeO2 up to 28 T. The dielectric dispersions in the three field-induced collinear-commensurate magnetic phases are well described by the superposition of Debye-type relaxations, and the number of contributions to the Debye-type dispersions differs in these phases.","" "Logarithmic temperature dependence of resistivity in CVD graphene","CVDグラフェンにおける抵抗のLog T依存性","Kanji Takehana, Yasutaka Imanaka, Eiichiro Watanabe, Hirotaka Oosato, Daiju Tsuya, Yongmin Kim, Ki-Seok An","Kanji Takehana, Yasutaka Imanaka, Eiichiro Watanabe, Hirotaka Oosato, Daiju Tsuya, Yongmin Kim, Ki-Seok An","Current Applied Physics","Current Applied Physics","17","4","474","478","2017-04-01","TRUE","","scientific_journal","eng","","10.1016/j.cap.2017.01.002","","Logarithmical increase of the longitudinal resistivity between 10 K and 80 K and its saturation at low temperature was observed in the graphene synthesized by the CVD with various applied gate voltage. In the two-dimensional system, it is considerably difficult to identify the origin of the logarithmic temperature (Log-T) increase of the resistivity, because there are three corrections to exhibit the Log-T behavior: the weak localization, the electron-electron interaction (EEI) in the disordered system and the Kondo effect. In order to distinguish the origin of the Log-T behavior, we contrived a new method utilizing the magnetotransport property in tilted magnetic fields. As a result, we have assigned the Log-T behavior in the CVD graphene to the correction of the EEI.","" "Spin-Driven Multiferroic Properties of PbMn7O12 Perovskite","Spin-Driven Multiferroic Properties of PbMn7O12 Perovskite","Alexei A. Belik, Yana S. Glazkova, Noriki Terada, Yoshitaka Matsushita, Alexey V. Sobolev, Igor A. Presniakov, Naohito Tsujii, Shigeki Nimori, Kanji Takehana, Yasutaka Imanaka","Alexei A. Belik, Yana S. Glazkova, Noriki Terada, Yoshitaka Matsushita, Alexey V. Sobolev, Igor A. Presniakov, Naohito Tsujii, Shigeki Nimori, Kanji Takehana, Yasutaka Imanaka","Inorganic Chemistry","Inorganic Chemistry","55","12","6169","6177","2016-06-20","TRUE","","scientific_journal","eng","","10.1021/acs.inorgchem.6b00774","","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 R-3 near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure with space group Im-3; the Im-3-to-R-3 transition is associated with charge ordering (CO). Below TOO = 294 K, a structural modulation transition takes place associated with orbital ordering (OO). There are two magnetic transitions with the Néel temperatures TN1 = 83 K and TN2 = 77 K and probably a lock-in transi","" "Activation of frozen ferroelectric domain wall by magnetic field sweeping in multiferroicCuFeO2","Activation of frozen ferroelectric domain wall by magnetic field sweeping in multiferroic CuFeO2","H. Tamatsukuri, S. Mitsuda, T. Nakajima, K. Shibata, C. Kaneko, K. Takehana, Y. Imanaka, N. Terada, H. Kitazawa, K. Prokes, S. Matas, K. Kiefer, S. Paeckel, A. Sokolowski, B. Klemke, S. Gerischer","H. Tamatsukuri, S. Mitsuda, T. Nakajima, K. Shibata, C. Kaneko, K. Takehana, Y. Imanaka, N. Terada, H. Kitazawa, K. Prokes, S. Matas, K. Kiefer, S. Paeckel, A. Sokolowski, B. Klemke, S. Gerischer","Physical Review B","Physical Review B","93","17","","","2016-05-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.93.174101","","In a ferroelectric helimagnetic phase of a spin-driven multiferroic, CuFeO2, we find irreversibly additive evolution of electric polarization P induced by sweeping magnetic field H under an applied electric field E, despite a large coercive electric field in the phase. From the unpolarized neutron diffraction experiments with in situ P measurements under applied E, we reveal that increment of P is achieved by the variation of an incommensurate magnetic modulation wave number q of the helical magnetic ordering in H sweeping regardless of increasing or decreasing H .","" "Ferroelectricity induced by ferriaxial crystal rotation and spin helicity in aB-site-ordered double-perovskite multiferroicIn2NiMnO6","Bサイト秩序ダブルペロブスカイト型化合物In2NiMnO6のferriaxial結晶歪みとスピンhelicity誘起強誘電性","Noriki Terada, Dmitry D. Khalyavin, Pascal Manuel, Wei Yi, Hiroyuki S. Suzuki, Naohito Tsujii, Yasutaka Imanaka, Alexei A. Belik","Noriki Terada, Dmitry D. Khalyavin, Pascal Manuel, Wei Yi, Hiroyuki S. Suzuki, Naohito Tsujii, Yasutaka Imanaka, Alexei A. Belik","Physical Review B","Physical Review B","91","10","","","2015-03-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.91.104413","","We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P ≃ 30 μC/m2 is observed in a polycrystalline sample below TN = 26 K where a magnetic phase transition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with “cycloidal” and “proper screw” components appears below TN, which has the incommensurate propagation vector k=(ka,0,kc;ka≃0.274, kc≃-0.0893). The established magnetic point group 21′ implies the macroscopic ferroelectric polarization to be along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii-Moriya effect allow us to specify two distinct contributions to the polariza- tion of In2NiMnO6. ","" "High-pressure synthesis, crystal structure and magnetic properties of TlCrO3 perovskite","High-pressure synthesis, crystal structure and magnetic properties of TlCrO3 perovskite","Wei Yi, Yoshitaka Matsushita, Yoshio Katsuya, Kazunari Yamaura, Yoshihiro Tsujimoto, Igor A. Presniakov, Alexey V. Sobolev, Yana S. Glazkova, Yuliya O. Lekina, Naohito Tsujii, Shigeki Nimori, Kanji Takehana, Yasutaka Imanaka, Alexei A. Belik","Wei Yi, Yoshitaka Matsushita, Yoshio Katsuya, Kazunari Yamaura, Yoshihiro Tsujimoto, Igor A. Presniakov, Alexey V. Sobolev, Yana S. Glazkova, Yuliya O. Lekina, Naohito Tsujii, Shigeki Nimori, Kanji Takehana, Yasutaka Imanaka, Alexei A. Belik","Dalton Transactions","Dalton Transactions","44","23","10785","10794","2015-02-17","TRUE","","scientific_journal","eng","","10.1039/c4dt03823a","","TlMO3 perovskites (M3+ = transition metals) are exceptional members of trivalent perovskite families because of the strong covalency of Tl3+–O bonds. Here we report on the synthesis, crystal structure and properties of TlCrO3 investigated by Mössbauer spectroscopy, specific heat, dc/ac magnetization and dielectric measurements. TlCrO3 perovskite is prepared under high pressure (6 GPa) and high temperature (1500 K) conditions. The crystal structure of TlCrO3 is refined using synchrotron X-ray powder diffraction data. Isothermal magnetization studies show that TlCrO3 is a fully compensated antiferromagnet similar to ScCrO3 and InCrO3, but different from RCrO3 (R3+ = Y and La–Lu). Ac and dc magnetization measurements with a fine step of 0.2 K reveal the existence of two N&ea","" "Hybrid White Light Emitting Diode Based on Silicon Nanocrystals","Hybrid White Light Emitting Diode Based on Silicon Nanocrystals","Batu Ghosh, Yoshitake Masuda, Yutaka Wakayama, Yasutaka Imanaka, Jun-ichi Inoue, Kenjiro Hashi, Kenzo Deguchi, Hideto Yamada, Yoshio Sakka, Shinobu Ohki, Tadashi Shimizu, Naoto Shirahata","Batu Ghosh, Yoshitake Masuda, Yutaka Wakayama, Yasutaka Imanaka, Jun-ichi Inoue, Kenjiro Hashi, Kenzo Deguchi, Hideto Yamada, Yoshio Sakka, Shinobu Ohki, Tadashi Shimizu, Naoto Shirahata","Advanced Functional Materials","Advanced Functional Materials","","","n/a","n/a","2014-09-01","TRUE","","scientific_journal","eng","","10.1002/adfm.201401795","","ダイヤモンド構造を有するシリコンナノ粒子に特徴付けられる発光特性を利用した電流注入型発光デバイス創製に関する。ナノ粒子の酸化を抑制したシリコン発光層を形成することで低電力駆動を実現した。発光スペクトル間の加成性を巧みに利用した新しい素子構造を有する白色発光ダイオードである。","" "Substrate dependence of cyclotron resonance on large-area CVD graphene","Substrate dependence of cyclotron resonance on large-area CVD graphene","K. Takehana, Y. Imanaka, T. Takamasu, Y. Kim, K.-S. An","K. Takehana, Y. Imanaka, T. Takamasu, Y. Kim, K.-S. An","Current Applied Physics","Current Applied Physics","14","","S119","S122","2014-03-01","TRUE","","scientific_journal","eng","","10.1016/j.cap.2013.11.010","","The magneto-transport measurements have been investigated on the CVD samples fabricated in the Hall-bar form of 10 m width. We observed that the longitudinal resistance (xx) increases logarithmically with decreasing temperature at wide temperature range up to several tens degree. The xx gradually saturate with decreasing temperature. This behavior is quite similar with that in the ion irradiated graphene which was argued to originate in the Kondo effect. In order to distinguish its origin, we have investigated the logarithmic behavior with applied high magnetic fields up to 15 T in-plain of the sample. As the results, we assigned that the logarithmic increase in the CVD graphene is unlikely to result in the Kondo effect, but in the presence of the disorder. ","" "Cyclotron Resonance in ZnO Heterostructures at High Magnetic Fields","Cyclotron Resonance in ZnO Heterostructures at High Magnetic Fields","Y. Imanaka","Y. Imanaka","Journal of Low Temperature Physics","Journal of Low Temperature Physics","170","5-6","389","396","2013-03-01","TRUE","","scientific_journal","eng","","10.1007/s10909-012-0775-4","","The carrier-density dependence of the cyclotron resonance was studied in ZnMgO/ZnO heterostructures between n = 5.4 × 1012 cm-2 and n = 7.5 × 1012 cm-2. The effective mass was obtained as m∗ = 0.32m0, and the significant carrier-density dependence of the effective mass was not observed in the present samples. This is partially due to the suppression of the resonant polaron effect in the dense carrier system. Oscillatory behavior appears in the cyclotron resonance spectra at the higher magnetic field side of the resonant field. The oscillatory period is perfectly coincident with the one of the Shubnikov-de Hass oscillation.","" "Magnetic property of pyrolytic carbon prepared on diamond powder in applied magnetic field","Magnetic property of pyrolytic carbon prepared on diamond powder in applied magnetic field","K. Kamishima, T. Tokue, D. Miyata, Y. Sato, F. Kadonome, T. Noda, K. Kakizaki, N. Hiratsuka, Y. Imanaka, T. Takamasu","K. Kamishima, T. Tokue, D. Miyata, Y. Sato, F. Kadonome, T. Noda, K. Kakizaki, N. Hiratsuka, Y. Imanaka, T. Takamasu","Journal of Magnetism and Magnetic Materials","Journal of Magnetism and Magnetic Materials","324","6","1106","1111","2012-03-01","TRUE","","scientific_journal","eng","","10.1016/j.jmmm.2011.10.042","","We have prepared pyrolytic carbon samples from triethylamine on diamond powder in applied magnetic field of 6 T and investigated their magnetic properties. A ferromagnetic sample was obtained from the pyrolysis products even at room temperature, with spontaneous magnetization of 6.4 A m2/kg at 300 K, which is twice as large as that of the sample prepared without diamond powder. Therefore, the diamond powder seems to promote the formation of a three-dimensional ferromagnetic structure in pyrolytic carbon. ","" "Cyclotron Resonance and Mass Enhancement by Electron Correlation inKFe2As2","Cyclotron Resonance and Mass Enhancement by Electron Correlation inKFe2As2","Motoi Kimata, Taichi Terashima, Nobuyuki Kurita, Hidetaka Satsukawa, Atsushi Harada, Kouta Kodama, Kanji Takehana, Yasutaka Imanaka, Tadashi Takamasu, Kunihiro Kihou, Chul-Ho Lee, Hijiri Kito, Hiroshi Eisaki, Akira Iyo, Hideto Fukazawa, Yoh Kohori, Hisatomo Harima, Shinya Uji","Motoi Kimata, Taichi Terashima, Nobuyuki Kurita, Hidetaka Satsukawa, Atsushi Harada, Kouta Kodama, Kanji Takehana, Yasutaka Imanaka, Tadashi Takamasu, Kunihiro Kihou, Chul-Ho Lee, Hijiri Kito, Hiroshi Eisaki, Akira Iyo, Hideto Fukazawa, Yoh Kohori, Hisatomo Harima, Shinya Uji","Physical Review Letters","Physical Review Letters","107","16","","","2011-10-01","TRUE","","scientific_journal","eng","","10.1103/physrevlett.107.166402","","Cyclotron resonance (CR) measurements in an Fe-based superconductor KFe2As2 (Tc ≈3.5 K) are performed in the frequency range between 55 and 82 GHz, and only one series of the CR signal is found. The field angle dependence of the resonance field shows that the CR signalarises from a two dimensional Fermi surface (FS). From the comparison with other measurements, the CR signal is attributed to the α FS centered at the Γ point of the Brillouin zone. The CR effective mass of (3.4±0.05)me (me is the free electron mass) is significantly smaller than that obtained from the de-Haas van Alphen (dHvA) oscillation measurements. This provides the direct evidence of the mass enhancement by the electron-electron (e-e) interaction.","" "Crystal Structure and Magnetic Properties of the Carbon-based Ferromagnet Prepared by Pyrolytic Method under High Magnetic Field","強磁場中熱分解法によって作製した炭素系強磁性体の結晶構造および磁気特性","徳江 将, 神島 謙二, 宮田 大資, 佐藤 佑樹, 柿崎 浩一, 平塚 信之, 今中 康貴, 高増 正","徳江 将, 神島 謙二, 宮田 大資, 佐藤 佑樹, 柿崎 浩一, 平塚 信之, 今中 康貴, 高増 正","粉体および粉末冶金","粉体および粉末冶金","58","3","176","180","2011-06-23","TRUE","","scientific_journal","jpn","","10.2497/jjspm.58.176","","","本研究では、物質材料研究機構強磁場ステーションに設置してある、大口径超伝導マグネットを用いた強磁場中熱分解法により炭素系強磁性体を作製した。" "Standardization of Excitation Efficiency in Near-field Scanning Optical Microscopy","Standardization of Excitation Efficiency in Near-field Scanning Optical Microscopy","Tadashi MITSUI, Yasutaka IMANAKA, Kanji TAKEHANA, Tadashi TAKAMASU, Ken NAKAJIMA, Jeongyong KIM","Tadashi MITSUI, Yasutaka IMANAKA, Kanji TAKEHANA, Tadashi TAKAMASU, Ken NAKAJIMA, Jeongyong KIM","Analytical Sciences","Analytical Sciences","27","2","139","142","2011-02-01","TRUE","","scientific_journal","eng","","10.2116/analsci.27.139","","日本分析化学会の英文誌であるAnalytical Sciences 誌の特集号”Advances in Scanning Probe Microscopies for Nanomaterial Analyses”において、近接場光学顕微鏡の国際標準化についての新規提案に関する論文である。本論文では、近接場光学顕微鏡技術における「ナノメートルスケール領域へのエネルギー集中効率、およびその検出効率」について論じており、開口型プローブの透過効率ではなく、プローブ先端に近接場光として発生している光エネルギーが、試料表面のみを励起させる点についても考慮して論じている。本論文の内容はそれ自体だけでなく、先行して国際標準化作業が進められている、近接場光学顕微鏡の空間分解能に関する標準を補強する役目も担っている。","" "Large Anisotropy in the Magnetic Susceptibility of Metallic Carbon Nanotubes","Large Anisotropy in the Magnetic Susceptibility of Metallic Carbon Nanotubes","T. A. Searles, Y. Imanaka, T. Takamasu, H. Ajiki, J. A. Fagan, E. K. Hobbie, J. Kono","T. A. Searles, Y. Imanaka, T. Takamasu, H. Ajiki, J. A. Fagan, E. K. Hobbie, J. Kono","Physical Review Letters","Physical Review Letters","105","1","","","2010-07-01","TRUE","","scientific_journal","eng","","10.1103/physrevlett.105.017403","","Through magnetic linear dichroism spectroscopy, the magnetic susceptibility anisotropy of metallic single-walled carbon nanotubes has been extracted and found to be 2–4 times greater than values for semiconducting nanotubes. This large anisotropy can be understood in terms of large orbital paramagnetism of metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in a parallel field, and our calculations quantitatively reproduce these results. We also compare our values with previous work for semiconducting nanotubes, which confirm that the magnetic susceptibility anisotropy does not increase linearly with the diameter for small-diameter nanotubes.","" "Cyclotron resonance of two-dimensional electron system affected by neighboring quantum dot layer","量子ドットー2次元電子結合系のサイクロトロン共鳴","K. Takehana, Y. Imanaka, T. Takamasu, M. Henini","K. Takehana, Y. Imanaka, T. Takamasu, M. Henini","Applied Physics Letters","Applied Physics Letters","96","19","193110","","2010-05-10","TRUE","","scientific_journal","eng","","10.1063/1.3430062","","We have investigated the cyclotron resonance (CR) in a two-dimensional electron system (2DES) separated by a thin barrier layer from InAs self-assembled quantum dots (QDs). Two absorption peaks of CR of the 2DES were clearly observed, indicating coexistence of free electrons with high mobility and trapped electrons within local potential minima caused by the neighboring QDs. The CR of the trapped electrons changes its intensity, corresponding to the charge state of the QDs. This is the first optical measurements to show that the charge state of the QDs affects on the 2DES in the role as a floating gate.","" "Effect of Charge State in Nearby Quantum Dots on Quantum Hall Systems","Effect of Charge State in Nearby Quantum Dots on Quantum Hall Systems","TAKEHANA, Kanji, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Mohamed Henini","TAKEHANA, Kanji, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Mohamed Henini","JOURNAL OF LOW TEMPERATURE PHYSICS","JOURNAL OF LOW TEMPERATURE PHYSICS","","","234","237","2010-04-01","TRUE","","scientific_journal","eng","","","","We have investigated the magnetoresistance and the cyclotron resonance of the gated two-dimensional electron system (2DES) separated by a thin barrier from a layer of InAs quantum dots (QDs), in order to investigate the influence of the electron charge state of the QDs on the transport properties of the nearby 2DES in quantum Hall regime. Clear features of both integer and fractional quantum Hall effect (QHE) were observed despite the proximity of the QD layer to the 2DES. On one sample, however, the magnetoresistance (Rxx) and Hall resistance were found to be significantly suppressed by same degree in the magnetic field range corresponding to filling factor nu < 1. when the nearby QDs were charged with electron . ","" "Cyclotron study of 2DES incorporating QD layer","Cyclotron study of 2DES incorporating QD layer","TAKEHANA, Kanji, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Mohamed Henini","TAKEHANA, Kanji, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Mohamed Henini","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","","","915","917","2010-02-01","TRUE","","scientific_journal","eng","","","","We haveinvestigatedthemagneto-transportpropertyandthecyclotronresonance(CR)ofatwo- dimensionalelectronsystem(2DES)separatedbyathinbarrierfromalayerofInAsself-assembled quantumdots(QDs)inthequantumHallregime.Themagnetoresistance ðrxxÞ and Hallresistance ðrxyÞ were suppressedsignificantlyat no1 whenapositivevoltagewasappliedtothefrontgate.Onthe other hand,cleartwoabsorptionlinesofCRoftheGaAs2DESwereobserved,indicatingcoexistenceof free-like-electronsandelectronstrappedbythelocalpotentialminimainthe2DES.SincetheCRofthe trapped electronsappearswhenthesuppressionof rxx and rxy occurs,weassignedittotheCRofthe electronswhichareinducedinthe2DESbythefunctionoftheQDsasafloatinggate.","" "Magnetotransport properties of Ytterbium doped AlxGa1-xAs/GaAs two-dimensional electron systems","YtterbiumドープAlxGa1-xAs/GaAs2次元電子系の磁気輸送特性","KAIZU, Toshiyuki, IMANAKA, Yasutaka, TAKEHANA, Kanji, TAKAMASU, Tadashi","KAIZU, Toshiyuki, IMANAKA, Yasutaka, TAKEHANA, Kanji, TAKAMASU, Tadashi","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","","","1126","1129","2010-02-01","TRUE","","scientific_journal","eng","","","","Rare-earth (RE) doped semiconductors are attractive materials for optical device applications because they show sharp and temperature-stable luminescence. For Ytterbium (Yb) doped AlxGa1-xAs, photoluminescence due to Yb intra-4f-shell transitions have been observed in the thin film and superlattice samples. In the luminescence mechanism of RE-doped semiconductors, it has been suggested that isoelectronic traps formed by the RE ions play a key role. However, the Yb-related trap state in AlxGa1-xAs is not well understood yet. In this study, we fabricated Yb-doped AlxGa1-xAs/GaAs two dimensional electron systems, which is sensitive to ionized impurity scattering, and investigated the magneto-transport properties.","" "Prepalation of pyrolytic magnetic carbon under magnetic field","磁場印加中熱分解による強磁場性熱分解炭素の作製","神島 謙二, 宮田 大資, 佐藤 佑樹, 徳江 将, 柿崎 浩一, 平塚 信之, 今中 康貴, 高増 正","神島 謙二, 宮田 大資, 佐藤 佑樹, 徳江 将, 柿崎 浩一, 平塚 信之, 今中 康貴, 高増 正","粉体および粉末冶金","粉体および粉末冶金","56","7","456","460","2009-07-29","TRUE","","scientific_journal","jpn","","10.2497/jjspm.56.456","","","通常、炭素を主成分とした有機物質では結合性軌道に反対向きのスピンを持つ電子が2個入る。したがって、ほとんどの有機物性は強磁場を示さない。しかし、近年、開殻不対電子を持つ有機物質で強磁場性磁気秩序を示すものが見出され、室温でも強磁性を示す事例も報告されている。その中で、我々は熱分解有機物に着目し、窒素を含む有機物(トリエチルアミン)を約900℃で熱分解する事により、微量(~mg)の強磁性炭素質試料が得られることを確認した。また、得られた熱分解炭素物質を磁場中で400℃以上熱処理することによって、磁化が上昇することを見出した。これらのことから、熱分解段階で磁場を印加した場合、強磁性試料の収量・磁化が増加されることが期待される。" "Possible Phase Transition Deep Inside the Hidden Order Phase of Ultraclean URu2Si2","Possible Phase Transition Deep Inside the Hidden Order Phase of Ultraclean URu2Si2","H. Shishido, K. Hashimoto, T. Shibauchi, T. Sasaki, H. Oizumi, N. Kobayashi, T. Takamasu, K. Takehana, Y. Imanaka, T. D. Matsuda, Y. Haga, Y. Onuki, Y. Matsuda","H. Shishido, K. Hashimoto, T. Shibauchi, T. Sasaki, H. Oizumi, N. Kobayashi, T. Takamasu, K. Takehana, Y. Imanaka, T. D. Matsuda, Y. Haga, Y. Onuki, Y. Matsuda","Physical Review Letters","Physical Review Letters","102","15","","","2009-04-01","TRUE","","scientific_journal","eng","","10.1103/physrevlett.102.156403","","To elucidate the underlying nature of the hidden order (HO) state in heavy-fermion compound URu2Si2,we measure electrical transport properties of ultraclean crystals in a high field, low temperature regime.Unlike previous studies, the present system with much less impurity scattering resolves a distinct anomaly of the Hall resistivity at H ¼ 22:5 T, well below the destruction field of the HO phase ’ 36 T. In addition, a novel quantum oscillation appears above a magnetic field slightly below H. These results indicate an abrupt reconstruction of the Fermi surface, which implies a possible phase transition wellwithin the HO phase caused by a band-dependent destruction of the HO parameter.","" "Magneto-optical properties of n-type modulation-doped (Cd,Cr)Te quantum well","Magneto-optical properties of n-type modulation-doped (Cd,Cr)Te quantum well","Fumiyoshi Takano, Takayuki Nishizawa, JeungWoo Lee, Shinji Kuroda, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Hiro Akinaga","Fumiyoshi Takano, Takayuki Nishizawa, JeungWoo Lee, Shinji Kuroda, IMANAKA, Yasutaka, TAKAMASU, Tadashi, Hiro Akinaga","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES","","","1166","1168","2008-03-01","TRUE","","scientific_journal","eng","","","","Magneto photoluminescence were studied in (CdCr)Te quantum well with 2DEGS at high magnetic fields. Magnetic field depndence of the optical spectra in circular polarization are quite similar to the one of CdTe quantume well.","" "Cyclotron resonance in II–VI semiconductors at THz region","II-VI族半導体のTHz領域におけるサイクロトロン共鳴","Y. Imanaka, T. Takamasu, K. Takehana, M. Oshikiri, G. Kido, H. Nojiri, Y. H. Matsuda, H. Arimoto, S. Takeyama, N. Miura, G. Karczewski, T. Wojtowicz, J. Kossut","Y. Imanaka, T. Takamasu, K. Takehana, M. Oshikiri, G. Kido, H. Nojiri, Y. H. Matsuda, H. Arimoto, S. Takeyama, N. Miura, G. Karczewski, T. Wojtowicz, J. Kossut","physica status solidi (b)","physica status solidi (b)","243","4","939","942","2006-03-01","TRUE","","scientific_journal","eng","","10.1002/pssb.200564719","","In this paper, we will discuss the electron CR in II-VI semiconductors (ZnO, ZnS, ZnSe, CdS, CdSe, CdTe) and Cd1-xMnxTe/CdMgTe 2DEGs at the wide range of the photon energy with the use of both pulsed magnets (up to 600T) and steady ones (up to 18T).","" "Photoluminescence of Yb3+-doped CuInS2 single crystals prepared by In-flux and chemical vapor transport methods","YbをドープしたCuInS2単結晶のフォトルミネセンス","TSUJII, Naohito, IMANAKA, Yasutaka, TAKAMASU, Tadashi, KITAZAWA, Hideaki, KIDO, Giyuu","TSUJII, Naohito, IMANAKA, Yasutaka, TAKAMASU, Tadashi, KITAZAWA, Hideaki, KIDO, Giyuu","JOURNAL OF ALLOYS AND COMPOUNDS","JOURNAL OF ALLOYS AND COMPOUNDS","","","791","795","2006-02-01","TRUE","","scientific_journal","eng","","","","We have grown bulk single crystals of Yb-doped CuInS2 by In-flux and chemical transport methods. Magnetic susceptibility measurements have shown the Yb-concentration to be 1*10^{18} ~ 3*10^{19} cm-3. Photoluminescence spectra have shown that the chemical transport grown crystals exhibit most pronounced Yb-related luminescence.","" "Stability of singlet and triplet charged excitons in CdTe/CdMgTe 2 dimensional electron systems around v=1","Stability of singlet and triplet charged excitons in CdTe/CdMgTe 2 dimensional electron systems around v=1","IMANAKA, Yasutaka, TAKAMASU, Tadashi, KIDO, Giyuu, J. Kossut, T. Wojtowicz, G. Karczewski","IMANAKA, Yasutaka, TAKAMASU, Tadashi, KIDO, Giyuu, J. Kossut, T. Wojtowicz, G. Karczewski","JOURNAL OF SUPERCONDUCTIVITY","JOURNAL OF SUPERCONDUCTIVITY","","","215","218","2005-04-01","TRUE","","scientific_journal","eng","","","","In this study, we have performed magneto-luminescence experiments of CdTe/CdMgTe quantum wells (QWs), which has high mobility, in the wide range of the carrier density between 1*10^11cm-2 and 6*10^11cm-2 at high magnetic fields up to 35T for investigating the evolution of the PL spectra and the stability of the (singlet and triplet) charged exciton. The PL spectra in our samples can be hence understood in terms of the charged exciton even in the high carrier density region.","" "Cyclotron resonance and faraday rotation in n-type CdS at high magnetic fields","超強磁場におけるn型CdSのサイクロトロン共鳴とファラデー回転","IMANAKA, Yasutaka, 野尻浩之, 松田康弘, 三浦登","IMANAKA, Yasutaka, 野尻浩之, 松田康弘, 三浦登","PHYSICA B-CONDENSED MATTER","PHYSICA B-CONDENSED MATTER","","","437","441","2004-05-01","TRUE","","scientific_journal","eng","","","","We have investigated cyclotron resonance (CR) and Faraday rotation (FR) in II-VI semiconductors at ultra-high magnetic fields, which are generated by the electromagnetic flux compression method and the single turn coil technique. In CR experiments, we investigated the effective mass in the wide range of the photon energy below and above the LO phonon energy with applying the magnetic field parallel or perpendicular to the c-axis of sample. In FR experiments, we succeeded to observe nonlinearity of the Faraday rotation angle at high magnetic fields around 100T employing the wavelength near the band gap energy of CdS.","" "Leakage current induced anomalies in the photoluminescence of GaAs coupled quantum wells","GaAs結合量子井戸における発光のリーク電流による異常","IMANAKA, Yasutaka, A. J. Shields, P. Atkinson, I. Farrer, D. A. Ritchie, M. Pepper","IMANAKA, Yasutaka, A. J. Shields, P. Atkinson, I. Farrer, D. A. Ritchie, M. Pepper","Physica Status Solidi (C)","Physica Status Solidi (C)","","","612","615","2004-02-01","TRUE","","scientific_journal","eng","","","","We study here PL spectroscopy and imaging experiments on GaAs/AlGaAs CQWs as a function of applied electric field and laser power. PL spectra recorded on the m-i-n+ structure as a function of applied voltage reveal a strong Stark shift of the SIE transition. The SIE is observed to anti-cross the direct exciton and dominate the PL at higher electric fields. In contrast the n+-i-n+ structure shows a much weaker shift of the PL peak with applied voltage. The shift is accompanied by a large electron leakage current through the n+-i-n+ diode. The experimental results suggest that the large leakage currents in n+-i-n+ diode should be considered for interpreting the behavior of the SIE in the coupled quantum wells.",""