論文 - 小堀 裕己
-
Line-Width of Quantum Limit Cyclotron Resonance. II. Impurity and Carrier-Carrier Scatterings in Ge, InSb and GaAs 査読あり
Hiromi Kobori, Tyuji Ohyama, Eizo Otsuka
journal of the physical society of japan 59 ( 6 ) 2164 - 2178 1990年
共著
Cyclotron Resonance Line-Width (CRLW) has been studied in the quantum limit for impurity and carrier-carrier scatterings in Ge, InSb and GaAs. Ionized impurity and neutral impurity (electron-neutral donor and electron-neutral acceptor) scatterings have been examined with impurity scatterings. The dependences on temperature and magnetic field of CRLW for these two scatterings are similar to each other. From our experimental results it becomes clear that CRLW is approximately (1) independent of temperature and (2) proportional to the inverse of the square root of magnetic field. Electron momentum cross section by neutral acceptor is noted to be some orders of magnitude less as compared with that by neutral donor even in the quantum limit. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.
DOI： 10.1143/JPSJ.59.2164
-
Quantum limit cyclotron resonance in p-GaAs 査読あり
H. Kobori, T. Ohyama, E. Otsuka
Solid State Communications 63 ( 2 ) 123 - 126 1987年7月
共著
Electron scattering by neutral acceptors has been studied through far infrared (λ=172 μm) cyclotron resonance on p-GaAs at 4.2 K. It is found that (1) The inverse relaxation time is considerably smaller in the quantum limit than that predicted by D.C. transport theory in the absence of a magnetic field. (2) The same increase linearly with neutral acceptor concentration. (3) The electron momentum transfer cross section by neutral acceptor is by more than an order of magnitude smaller than that by neutral donor even in the quantum limit. © 1987.
-
Bulk-sensitive photoemission spectroscopy of TlFe<inf>2</inf>Se<inf>2</inf>
Y. Nishitani, A. Okada, A. Higashiya, A. Irizawa, T. Muro, S. Horiguchi, H. Sato, N. Umeyama, N. Miyakawa, S. I. Ikeda, H. Kobori, A. Yamasaki
Journal of Physics: Conference Series 391 ( 1 ) 2012年
共著
We have investigated the electronic structures of the parent compound of an iron chalcogenide superconductor TlFe2Se2 by bulk-sensitive photoemission spectroscopy (PES). Valence-band PES demonstrates the energy gap opening at the Fermi level due to the shift of Fe 3d state to the higher binding energy side as compared to the calculated density of states, being consistent with the insulating behaviour in transport measurements. © Published under licence by IOP Publishing Ltd.
-
Electronic structures of the FeSe superconductor studied by high-energy photoelectron spectroscopy
A. Yamasaki, Y. Matsui, S. Imada, K. Takase, H. Azuma, T. Muro, Y. Kato, A. Sekiyama, S. Suga, A. Higashiya, M. Yabashi, K. Tamasaku, T. Ishikawa, K. Terashima, H. Kobori, A. Sugimura, N. Umeyama, H. Sato, Y. Hara, N. Miyakawa, S. I. Ikeda
Journal of Physics: Conference Series 391 ( 1 ) 2012年
共著
The bulk electronic structures of an iron-based superconductor FeSe have been investigated by photoelectron and photoabsorption spectroscopies (PES and XAS) with use of high-energy photons (hν 0.7-0.9 and 8 keV). The core-level PES and XAS combined with the configuration interaction cluster model calculation reveal the highly coherent nature of the Fe 3d electrons which is realized by the hybridization between Fe 3d and Se 4p states. © Published under licence by IOP Publishing Ltd.
-
Electrical- and magneto-resistance control for magnetite nanoparticle sinter by regulation of heat treatment temperature
H. Kobori, T. Asahi, A. Yamasaki, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh and T.Shimizu
Journal of Magnetism and Magnetic Materials 323 686 - 689 2011年
共著
担当区分：筆頭著者
-
Spin-dependent-magnetoresistance control by regulation of heat treatment temperature for magnetite nano-particle sinter 査読あり
H. Kobori, T. Asahi, A. Yamasaki, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh, T. Shimizu
Annalen der Physik (Leipzig) 18 ( 12 ) 935 - 938 2010年12月
共著
The control of spin-dependent-magnetoresistance by regulation of the heat treatment (HT) temperature for magnetite (Fe3O3) nano-particle sinter (MNPS) has been studied. The average nano-particle size in the MNPS is 30nm and the HT was carried out from 400° C to 800°C. The HT of the MNPS varies the coupling form, between adjacent magnetite nano-particles and the crystallinity of that. The measurements on electrical resistance (ER), magnetoresistance (MR) and magnetization were performed between 4K and 300K. The behavior of the ER and MR considerably changes at the HT temperature of ∼600°C. Below ∼600°C the ER indicates the variable-range-hopping conduction behavior and the MR shows the large intensity in a wide temperature region. Above ∼600°C the ER shows the indication of the Verwey transition near 110K like a bulk single crystal and the MR designates the smaller intensity. We consider that below ∼600°C the ER and MR are dominated by the grain-boundary conduction and above ∼600° C those are determined by the inter-grain conduction. The magnetic field application to the grain-boundary region is inferred to cause the large enhancement of the MR. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA,.
-
Electron correlation in the FeSe superconductor studied by bulk-sensitive photoemission spectroscopy
A. Yamasaki, Y. Matsui, S. Imada, K. Takase, H. Azuma, T. Muro, Y. Kato, A. Higashiya, A. Sekiyama, S. Suga, M. Yabashi, K. Tamasaku, T. Ishikawa, K. Terashima, H. Kobori, A. Sugimura, N. Umeyama, H. Sato, Y. Hara, N. Miyagawa, S. I. Ikeda
Physical Review B - Condensed Matter and Materials Physics 82 ( 18 ) 2010年11月
共著
We have investigated the electronic structures of recently discovered superconductor FeSe by soft-x-ray and hard-x-ray photoemission spectroscopy with high-bulk sensitivity. The large Fe3d spectral weight is located in the vicinity of the Fermi level (EF), which is demonstrated to be a coherent quasiparticle peak. Compared with the results of the band-structure calculation with local-density approximation, Fe3d band narrowing and the energy shift of the band toward EF are found, suggesting an importance of the electron correlation effect in FeSe. The self-energy correction provides the larger mass enhancement value (Z-1 ≃3.6) than in Fe-As superconductors and enables us to separate an incoherent part from the spectrum. These features are quite consistent with the results of recent dynamical mean-field calculations, in which the incoherent part is attributed to the lower Hubbard band. © 2010 The American Physical Society.
-
Structure-Disorder induced Magneto-Resistance Intensification on Spin-Dependent-Conduction in Magnetite (Fe3O4) Thin Film produced by RF Magnetron Sputtering Method（共著） 査読あり
H. Kobori, D. Shimizu, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh and T. Shimizu
J. Phys.: Conf. Ser. 150 022042-1 - 022042-4 2009年
共著
担当区分：筆頭著者
J. Phys.: Conf. Ser. 150 Vol. 150 (2009) pp.022042
-
Nanomanipulation of Single Nanoparticle Using a Carbon Nanotube Probe in a Scanning Electron Microscope 査読あり
H. Suga, Y. Naitoh, M. Tanaka, M. Horikawa, H. Kobori and T. Shimizu
Applied Physics Express 2 ( 5 ) 055004-1 - 055004-4 2009年
共著
-
Magneto-Resistance Control by use of Interparticle-Coupling- Form Variation in Half-Metallic Magnetite Nano-Particle Sinter 査読あり
T. Asahi, H. Kobori, A. Yamasaki, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh and T. Shimizu
Journal of Physics: Conference Series 150 022004-1 - 022004-4 2009年
共著
-
Spin-dependent-magnetoresistance control by regulation of heat treatment temperature for magnetite nano-particle sinter 査読あり
H. Kobori, T. Asahi, A. Yamasaki, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y.Naitoh, and T. Shimizu
Annals of Physics 18 ( 12 ) 935 - 938 2009年
共著
担当区分：筆頭著者
-
Magneto-resistance control by use of interparticle-coupling-form variation in half-metallic magnetite nano-particle sinter 査読あり
T. Asahi, H. Kobori, A. Yamasaki, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh, T. Shimizu
Journal of Physics: Conference Series 150 ( 2 ) 2009年
共著
We have studied the magneto-resistance (MR) control by use of a variation of the interparticle-coupling-form (IPCF) in half-metallic magnetite (Fe 3O4) nano-particle sinter (MNPS). The average nano-particle size of the MNPS is 30nm and the measurements were carried out between 4K and 300K. The variation of the IPCF in the MNPS was performed by the heat treatment (HT) between 400°C and 800°C. The behavior of the MR and electrical resistance (ER) considerably changes at the HT temperature of around 600°C. Below around 600°C the ER indicates the variable-range-hopping conduction behavior in a wide temperature region, whereas above around 600°C the ER shows the indication of the Verwey transition near 110K like a bulk single crystal. We have considered that the electrical conduction switching in the MNPS occurs at the HT temperature of around 600°C. Namely, below around 600°C the ER is dominated by the grain-boundary conduction and above around 600°C the ER is determined by the inter-grain conduction. We have found that at room temperature the MR for the MNPS made at the HT temperature of 400°C shows approximately 20 times that of a bulk single crystal. The application of the magnetic field to grain-boundary conduction is considered to cause the large enhancement of the MR. © 2009 IOP Publishing Ltd.
-
Structure-Disorder induced Magneto-Resistance intensification on spin-dependent-conduction in magnetite (Fe<inf>3</inf>O<inf>4</inf>) thin film produced by RF magnetron sputtering method 査読あり
H. Kobori, D. Shimizu, A. Sugimura, T. Taniguchi, A. Ando, H. Kawanaka, Y. Naitoh, T. Shimizu
Journal of Physics: Conference Series 150 ( 2 ) 2009年
共著
The intensification of magneto-resistance (MR) caused by structure-disorder has been observed in magnetite (Fe3O4) thin film (MTF) produced by the rf magnetron sputtering method. The MTFs with the thickness of 20nm, 50nm and 100nm were deposited on the substrates of SiO2-glass, MgAl2O4 (100) and MgO (100) single crystals. We have observed that the MR of the MTF on SiO2-glass substrate changes 3-5 times larger than that of the MTFs on MgAl2O4 and MgO substrates. From the AFM, SEM and XRD measurements, we have found that the MTFs are composed of magnetite nano-particles (MNPs) and the crystal-axis directions of the MNPs in the MTF on SiO2-glass are mutually random and those of the MTFs on MgAl2O4 and MgO are almost aligned along (100) direction. In addition, from the electrical and magnetization measurements, we have found that the MNPs in the MTF on SiO2-glass show the amorphous-like behavior and those of the MTFs on MgAl2O 4 and MgO indicate the crystal-like behavior. © 2009 IOP Publishing Ltd.
-
Soft x-ray magnetic circular dichroism study of magnetite nanoparticles
A. Yamasaki, H. Kobori, H. Osawa, T. Nakamura, A. Sugimura
Journal of Physics: Conference Series 150 ( 4 ) 2009年
共著
The magnetic circular dichroism in the soft-x-ray core-level absorption (XMCD) of magnetite nanoparticles has been studied. The XMCD spectrum at the Fe L2,3 edge closely resembles the reported one of bulk single crystals in shape. This suggests that the derived amorphous-like grain boundary and the size effect of the magnetite crystals do not significantly affect the electronic structures and the local magnetism of Fe ions. It is also found that the orbital magnetic moment on Fe ions is rather small or quenched. © 2009 IOP Publishing Ltd.
-
Stability of electronic states across the metal-insulator transition in Pr Ru4 P12
A. Yamasaki, S. Imada, A. Sekiyama, H. Fujiwara, M. Yano, J. Yamaguchi, G. Funahashi, H. Sugawara, D. Kikuchi, H. Sato, T. Muro, A. Higashiya, K. Tamasaku, M. Yabashi, H. Kobori, A. Sugimura, T. Ishikawa, H. Harima, S. Suga
Physical Review B - Condensed Matter and Materials Physics 77 ( 16 ) 2008年4月
共著
We have investigated the exotic metal-insulator (M-I) transition in Pr Ru4 P12 by using hard-x-ray and soft-x-ray photoemission spectroscopies. The significantly large hybridization strength between conduction and Pr 4f electrons (c-f) is found not to change much between the metal and insulating phases. These results suggest that the M-I transition does not noticeably affect the c-f hybridization nature and P 3p-Pr 4f mixed states are highly stable. © 2008 The American Physical Society.
-
Spin-Dependent-Transport for Magnetite (Fe3O4) Thin Films on SiO2-Glass, MgO and MgAl2O4 Substrates prepared by RF-Magnetoron-Sputtering（共著） 査読あり
H. Kobori, D. Shimizu, A. Yamasaki, A. Sugimura, T. Taniguchi, H. Kawanaka, A. Ando and T. Shimizu
Proceedings of International Conference on Magnetic Materials 2007 22 - 24 2008年
共著
担当区分：筆頭著者
-
Magnetoresistance Enhancement of Halfmetal Magnetite (Fe3O4) Thin Film on SiO2-Glass Substrate prepared by RF-Magnetoron-Sputtering 査読あり
D. Shimizu, H. Kobori, A. Yamasaki, A. Sugimura, T. Taniguchi, H. Kawanaka, A. Ando and T. Shimizu
Proceedings of International Conference on Magnetic Materials 2007 19 - 21 2008年
共著
-
Drastic magnetoresistance enhancement on spin-dependent-transport and appearance of spin-glass-like behavior for magnetite nanoparticle sinter calcined at low temperature 査読あり
H. Kobori, K. Ohnishi, A. Sugimura, T. Taniguchi
AIP Conference Proceedings 893 1261 - 1262 2007年
共著
We have studied the spin-dependent-transport and magnetization for magnetite nanoparticle sinter (MNPS) calcined at low temperature. As compared with a bulk crystal, the drastic enhancement of negative differential magnetoresistance has been obtained for the MNPS. Below the Verwey transition temperature, we have observed the difference of magnetization between zero-field-cooling and field-cooling. This phenomenon indicates that localized spins in amorphous-like grain-boundary region in the MNPS are spin-glass-like. © 2007 American Institute of Physics.
DOI： 10.1063/1.2730359
-
Spatial fluctuation enhancement and nonradiative-recombination-center generation due to high Si-doping into GaAs/AlAs short-period-superlattices 査読あり
H. Kobori, A. Shigetani, I. Umezu, A. Sugimura
Physica B: Condensed Matter 376-377 ( 1 ) 861 - 863 2006年4月
共著
Through the time-resolved photoluminescence (TR-PL) measurement for excitons, we have studied the enhancement of spatial fluctuation (SF) and the generation of nonradiative-recombination-centers (NRC) due to high Si-doping into GaAs/AlAs short-period-superlattices (SPS's). We have carried out the exciton transport analysis according to Krivorotov et al. [I.N. Krivorotov, T. Chang, G.D. Gilliland, L.P. Fu, K.K. Bajaj, Phys. Rev. B 58 (1998) 10687]. From this analysis, we have obtained the temperature dependence of the exciton diffusivity, the concentration of the NRC and the average distant between adjacent localized states of excitons. The temperature dependence of the exciton diffusivity is found to be given by the sum of the temperature-independent contribution and the activation-type contribution. For the exciton diffusivity in undoped GaAs/AlAs SPS's, only the activation-type contribution has been observed. Therefore, we point out the possibility that the temperature-independent contribution comes from the tunneling through the impurities. In this experiment, the activation energy and the concentration of the NRC are found to be larger than those of undoped GaAs/AlAs SPS's. We infer that high Si-doping into GaAs/AlAs SPS causes the enhancement of the SF and the generation of NRC. © 2006 Elsevier B.V. All rights reserved.
-
Reversal magnetoresistance and unusual localized-spin freezing in magnetite sinter made from low size-dispersion hematite nano-particles with high temperature calcination（共著）
H. Kobori, K. Ohnishi, A. Sugimura and T. Taniguchi
Physica Status Solidi (c) 12 4204 - 4207 2006年
共著
担当区分：筆頭著者