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Photoinduced magnetic bound state in an itinerant correlated electron system with a spin-state degree of freedom

Physical Review B 2012年第4期86卷 045137-045137页

作者： Yu Kanamori Jun Ohara Sumio Ishihara Department of Physics Tohoku University Sendai 980-8578 Japan Core Research for Evolutional Science and Technology (CREST) Sendai 980-8578 Japan

The photoexcited state in a correlated electron system with a spin-state degree of freedom is studied. We start from the two-orbital extended Hubbard model where the energy difference between the two orbitals is introduced. The photoexcited metastable state is examined based on the effective model Hamiltonian derived using the two-orbital Hubbard model. Spin-state change is induced by photoirradiation in the low-spin band insulator near the phase boundary, and it is found that a high-spin state is stabilized by creating a ferromagnetic bound state with photodoped hole carriers. An optical absorption occurs between the bonding and antibonding orbitals inside the bound state. The time evolution of photoexcited states is simulated in the time-dependent mean-field scheme. It is found that pair annihilations of photodoped electrons and holes generate the high-spin state in a low-spin band insulator. We propose that this process is directly observed by the time-resolved photoemission experiments.

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Beamlike polarization entangled photon pairs generation by 2x2 fiber

Beamlike polarization entangled photon pairs generation by 2...

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High Intensity Lasers and High Field Phenomena, HILAS 2012

作者： Lo, Hsin-Pin Yabushita, Atsushi Luo, Chih-Wei Chen, Pochung Kobayashi, Takayoshi Department of Physics National Tsing Hua University Hsinchu 300 Taiwan Department of Electrophysics National Chiao-Tung University Hsinchu 300 Taiwan Core Research for Evolutional Science and Technology Japan Science and Technology Agency 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan University of Electro-Communications 1-5-1 Chofugaoka Chofu Tokyo 182-8585 Japan Institute of Laser Engineering Osaka University 2-6 Yamada oka Suita Osaka 565-0971 Japan

Beamlike photon pairs generated by pumping the Type-II BBO crystal. Then inserting into the 2x2 fiber, the polarization entangled photon pairs be measured from the output. © 2011 Optical Society of America.

ISBN: (纸本)9781557529398

关键词： Polarization

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Abrupt change in the energy gap of superconducting Ba1−xKxFe2As2 single crystals with hole doping

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Physical Review B 2012年第16期86卷 165117-165117页

作者： W. Malaeb T. Shimojima Y. Ishida K. Okazaki Y. Ota K. Ohgushi K. Kihou T. Saito C. H. Lee S. Ishida M. Nakajima S. Uchida H. Fukazawa Y. Kohori A. Iyo H. Eisaki C.-T. Chen S. Watanabe H. Ikeda S. Shin Institute for Solid State Physics (ISSP) University of Tokyo Kashiwa-no-ha Kashiwa Chiba 277-8581 Japan Transformative Research-project on Iron Pnictides (TRIP) Japan Science and Technology Agency (JST) Chiyoda-ku Tokyo 102-0075 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST) Chiyoda-ku Tokyo 102-0075 Japan National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Ibaraki 305-8568 Japan Department of Physics Chiba University Chiba 263-8522 Japan Department of Physics University of Tokyo Tokyo 113-8656 Japan Beijing Center for Crystal Research and Development Chinese Academy of Science (CAS) Zhongguancun Beijing 100190 China Department of Physics Kyoto University Sakyo-ku Kyoto 606-8502 Japan

We performed a laser angle-resolved photoemission spectroscopy (ARPES) study on a wide doping range of Ba1−xKxFe2As2 (BaK) and precisely determined the doping evolution of the superconducting gaps in this compound. The gap size of the outer hole Fermi-surface (FS) sheet around the Brillouin zone (BZ) center shows an abrupt drop with overdoping (for x≳ 0.6) while the inner and middle FS gaps roughly scale with Tc. This is accompanied by the simultaneous disappearance of the electron FS sheet with similar orbital character at the BZ corner. These results indicate the different contributions of X2−Y2 and XZ/YZ orbitals to superconductivity in BaK and can hardly be completely reproduced by the available theories on iron-based superconductors.

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Ambipolar transport in bulk crystals of a topological insulator by gating with ionic liquid

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Physical Review B 2012年第7期86卷 075306-075306页

作者： Kouji Segawa Zhi Ren Satoshi Sasaki Tetsuya Tsuda Susumu Kuwabata Yoichi Ando Institute of Scientific and Industrial Research Osaka University Ibaraki Osaka 567-0047 Japan Frontier Research Base for Global Young Researchers Graduate School of Engineering Osaka University 2-1 Yamada-oka Suita Osaka 565-0871 Japan Department of Applied Chemistry Graduate School of Engineering Osaka University 2-1 Yamada-oka Suita Osaka 565-0871 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST) Kawaguchi Saitama 332-0012 Japan

We report that the ionic-liquid gating of bulk single crystals of a topological insulator can control the type of the surface carriers and even results in ambipolar transport. This was made possible by the use of a highly bulk-insulating BiSbTeSe2 system where the chemical potential is located close to both the surface Dirac point and the middle of the bulk band gap. Thanks to the use of ionic liquid, the control of the surface chemical potential by gating was possible on the whole surface of a bulk three-dimensional sample, opening new experimental opportunities for topological insulators. In addition, our data suggest the existence of a nearly reversible electrochemical reaction that causes bulk carrier doping into the crystal during the ionic-liquid gating process.

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Polymer-Protected and Au-Containing Bi- and Trimetallic Nanoparticles as Novel Catalysts for Glucose Oxidation

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Macromolecular Symposia 2012年第1期317-318卷

作者： Naoki Toshima Haijun Zhang Department of Applied Chemistry Tokyo University of Science Yamaguchi SanyoOnoda Yamaguchi 756-0884 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST) Kawaguchi Saitama 332-0012 Japan

Polymer-protected metal nanoparticles (NPs) are recognized as a type of complex between a polymer and metal NPs, since the metal NPs are stabilized by coordination to the polymer. Thus, they can work as an effective catalyst in a dispersed state due to their high surface area-to-volume ratio and high stability by protection with poly(N-vinyl-2-pyrrolidone) (PVP). In this study, colloidal dispersions of PVP-protected and Au-containing bi- and trimetallic NPs were prepared and applied to the catalyst for the aerobic oxidation of glucose into gluconic acid in an alkaline solution. The AuAg and AuPt bimetallic NPs were more active than the Au NPs although the Ag and Pt NPs were less active than the Au NPs. The AuAgPt (Au/Ag/Pt = 7/2/1) trimetallic NPs were the most active catalyst for the same reaction. The high activity can be explained by electronic charge transfer from the Ag or Pt to the Au.

关键词： Ag Au catalyst bimetallic nanoparticles gluconic acid glucose oxidation Pt trimetallic nanoparticles

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Photoinduced Change in the Spin State of Itinerant Correlated Electron Systems

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Physical Review Letters 2011年第16期107卷 167403-167403页

作者： Y. Kanamori H. Matsueda S. Ishihara Department of Physics Tohoku University Sendai 980-8578 Japan Sendai National College of Technology Sendai 989-3128 Japan Core Research for Evolutional Science and Technology (CREST) Sendai 980-8578 Japan

A photoinduced spin-state change in the itinerant correlated electron system is studied. A photon introduced in the low-spin band insulator induces a bound state of the high-spin state and a photoexcited hole. This bound state brings a characteristic peak in the pump-probe optical absorption spectra which are completely different from the spectra in thermal-excited states. The present results well explain the recent experiments of the ultrafast optical spectroscopy in perovskite cobaltites.

关键词： Excited states

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Beamlike polarization entangled photon pairs generation by 2x2 fiber

Beamlike polarization entangled photon pairs generation by 2...

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High Intensity Lasers and High Field Phenomena, HILAS 2011

ISBN: (纸本)9781557529046

关键词： Polarization

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Terahertz Wave Emission from Intrinsic Josephson Junctions in Bi2Sr2CaCu2O8+δ

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Journal of physics: Conference Series 2012年第2期400卷

作者： K Kadowaki T Kashiwagi H Asai M Tsujimoto M Tachiki K Delfanazari R A Klemm Institute of Materials Science and Graduate School of Pure & Applied Sciences University of Tsukuba 1-1-1 Tennodai Tsukuba Ibaraki 305-8573 Japan WPI-MANA satellite National Institute for Materials Science(NIMS) 1-1 Namiki Tsukuba Ibaraki 305-0044 JAPAN Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST) Sanban-cho Bldg. 4F 5 Sanban-cho Chiyoda-ku Tokyo 102-0075 Japan Department of Physics Bldg. 121 PS 402 University of Central Florida 4000 Central Florida Blvd. Orlando FL 32816-2385 USA

We have studied the conditions for the THz radiation in many systems with different shapes and dimensions such as rectangles, squares, cylinders and (equilateral and isosceles including right-angled isosceles) triangles and rectangles with non-uniform width (asymmetric rectangles) fabricated from single crystals of Bi2Sr2CaCu2O8+δ, which are known as a typical intrinsic Josephson junction system. As a result two conditions have been deduced to be fulfilled: one is the ac-Josephson effect always working at each intrinsic Josephson junction. Another one is the standing wave formation of the THz waves excited inside the mesa due to the cavity resonance for the radiation. The former condition is always necessary for the radiation but the latter may have only the secondary role for the radiation because the Q-value of the resonance cavity in some cases seems to be quite low and of order of unity. Therefore, the radiation frequency can be controlled by the voltage effectively and widely varied by the ac-Josephson effect only. In addition, we show a new phenomenon observed at high current region and a comprehensive physical picture for the extraordinary THz radiation phenomenon is given.

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Continuous-wave photoinduced absorption studies in polythiophene and fullerene blended thin films

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Physical Review B 2011年第3期83卷 035305-035305页

作者： Takashi Kobayashi Keita Kinoshita Takashi Nagase Hiroyoshi Naito Department of Physics and Electronics Osaka Prefecture University 1-1 Gakuencho Sakai Osaka 599-8531 Japan The Research Institute for Molecular Electronic Devices Osaka Prefecture University 1-1 Gakuencho Sakai Osaka 599-8531 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency (JST) Japan

The generation and recombination dynamics of photocarriers (polarons) in poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester blended thin films have been investigated by means of continuous-wave photoinduced absorption spectroscopy. Continuous-wave photoinduced absorption spectroscopy has the advantage of being used to investigate long-lived excited species with lifetimes that range from microseconds to milliseconds. In this time range, three kinds of excited species are recognized in the blends: trapped, mobile, and delocalized polarons. From the modulation-frequency dependence, the mean lifetimes of the three types of polarons at low temperature were estimated. It is known that polarons are not generated directly by the pump beam but rather through Coulombically bound radical pairs. We have found that this two-step model for polaron generation can be recognized on a microsecond time scale by continuous-wave photoinduced absorption measurements.

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Ultrafast Time-Resolved Spectroscopy of PYP by a Sub-8fs Pulse at 400 nm

Ultrafast Time-Resolved Spectroscopy of PYP by a Sub-8fs Pul...

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第三届亚洲光谱会议

作者： J.Liu A.Yabushita S.Taniguchi T.Kobayashi State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine MechanicsChinese Academy of Sciences Advanced Ultrafast Laser Research Center University of Electro-Communications Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Agency Department of Electrophysics Chiao Tung University Institute for Laser Technology Osaka University

Ultrafast time-resolved PYP was studied by pump-probe spectroscopy using a sub-8 fs pulse laser with a central wavelength at 400 nm[1].The broadband spectrum of the UV pulse allowed us to detect the pump-probe signal over a broad spectral range in UV covering 360-440nm.A 128-channel detector array was used to simultaneously obtain the

关键词： PYP Ultrafast Time-Resolved Spectroscopy of PYP by a Sub-8fs Pulse at 400 nm

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