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Pacific Rim Conference on Lasers and Electro-Optics (CLEO/Pacific Rim)

作者： Liming Li S. Kusaka N. Karasawa R. Morita M. Yamashita Hokkaido University Japan Science and Technology Corporation Chitosc Japan Department of Applied Physics Core Research for Evolutional Science and Technology Sapporo Japan

The amplitude and phase of 5.0-fs optical pulses were characterized by a spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. This is the shortest pulse ever measured by the SPIDE... 详细信息

关键词： Optical pulses Optical interferometry Pulse measurements Pulse modulation Pulse amplifiers Optical pulse generation Optical modulation Chirp Delay Physics

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Semiconductor photonic crystals for lasers and functional devices

Semiconductor photonic crystals for lasers and functional de...

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IEEE Photonics Conference (IPC)

作者： M. Imada S. Noda Core Research of Evolutional Science and Technology Japan Science and Technology Corporation Kyoto Japan Department of Electronic Science and Engineering Kyoto University Kyoto Japan

We have demonstrated unique devices and phenomena utilizing 2D photonic crystals. In this presentation, we mainly report on 2D photonic crystal lasers and defect-based devices using 2D photonic crystal slabs. These re... 详细信息

关键词： Photonic crystals Semiconductor lasers Surface emitting lasers Diffraction Slabs Optical surface waves Wavelength measurement Laser theory Geometrical optics Photonic band gap

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Ultrafast spin relaxation of excitons in a self-organized quantum-well material

Ultrafast spin relaxation of excitons in a self-organized qu...

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Quantum Electronics and Laser science Conference (QELS)

作者： J. Ishi Y. Kato K. Ohashi H. Kunugita K. Ema T. Ban T. Kondo Department of Physics Sophia University Chiyoda Tokyo Japan Core Research For Evolutional Science and Technology (CREST) Japan Science and Technology Corporation Japan

Summary form only given. Time-resolved photoluminescence and pump-probe spectroscopies have been employed to study the spin relaxation processes of excitons in bulk semiconductors and semiconductor quantum wells (QWs). Extensive studies have shown that the spin dynamics in QWs differs from that in the bulk. In spite of many studies on excitons with large Bohr-radius such as in GaAs-based QWs, studies on excitons with small Bohr-radius are lacking. Since spin relaxation greatly depends on the exchange interaction between electron and hole in the exciton, the spin dynamics is expected to change with the coupling strength between the electron and hole. Therefore, experiments for excitons with small Bohr-radius are desired for full understanding of spin phenomena in QWs.

关键词： Excitons Quantum wells Optical pumping Probes Nonlinear optics Ultrafast optics Optical pulses Magnetic confinement Delay Lattices

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Diamond layers for active electronic devices

Diamond layers for active electronic devices

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International Conference on Novel Applications of Wide Bandgap Layers

作者： H. Okushi CREST JST Core Research for Evolutional Science and Technology of Japan Science and Technology Corporation Waseda University Japan Research Center of Advanced Carbon National Institute for Advanced Industrial Science and Technology Tsukuba Japan

This paper reviews our recent achievements in homoepitaxial CVD diamond layers for electronic devices. We have successfully synthesized high quality homoepitaxial diamond layers with atomically flat surface by the microwave plasma chemical vapor deposition (CVD) using a low CH4 concentration of CH4/H2 gas system less than 0.15% CH4/H2 ratio and Ib (001) substrates with low-misorientation angle less than 1.5°. These layers have atomically flat and have excellent electrical and optical properties. For example, highquality Schottky junctions between Al and p-type high-conductivity layer near the surface of these layers have been obtained. Based on this growth method, we have also successfully synthesized B-doped diamond layers using trimethylboron [B(CH3)3,TMB] gas as a B doping source, whose Hall mobility is 1840 cm 2 /Vs at 290 K. Schottky junctions fabricated by the B-doped diamond also show excellent performances, indicating that the quality of these diamond layers is device grade.

关键词： Atomic layer deposition Substrates Surface morphology Doping Chemical technology Atom optics Diamond-like carbon

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Generation of broadband (-1 GHz) sub-Poissonian-lights in light-emitting diodes at low photon-flux levels

Generation of broadband (-1 GHz) sub-Poissonian-lights in li...

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Pacific Rim Conference on Lasers and Electro-Optics (CLEO/Pacific Rim)

作者： K. Tanaka Y. Kadoya R. Masuyama H. Yuji M. Yamanishi Department of Physical Electronics Faculty of Engineering and Hiroshima-Branch of Research Project of Core Research of Evolutional Science and Technology JST Hiroshima University Higashihiroshima Japan

We present a broadband (near dc to 1 GHz) squeezing of intensity-fluctuation below the shot-noise-limited level in light-emitting diodes at low-photon flux level (photo current /spl sim/40 /spl mu/A).

关键词： Light emitting diodes Noise level Frequency estimation Bandwidth Optimized production technology Frequency measurement Noise measurement Low-frequency noise Solids Thermionic emission

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Generation of broadband sub-Poissonian-light in light-emitting diodes

Generation of broadband sub-Poissonian-light in light-emitti...

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Conference on Lasers and Electro-Optics (CLEO)

作者： K. Tanaka Y. Kadoya H. Yuji R. Masuyama M. Yamanishi Department of Physical Electronics Faculty of Engineering and Hiroshima Branch of Research Project for Core Research for Evolutional Science and Technology JST Hiroshima University Higashihiroshima Hiroshima Japan

Summary form only given. Generally, light-emitting diodes (LEDs) are considered to be low-performance devices in comparison with laser diodes (LDs). However, for future applications such as the parallel inter- or intra-integrated-circuit chip optical-connections, where very low power-consumption is required for the light emitters, a LED can be a very attractive device because of the threshold-free input-output characteristics. So far, continuous efforts have been made to improve the performance of LEDs. In this paper, we focus on another very important aspect, i.e. the noise characteristics. In comparison with LDs, in general, LEDs exhibit excellent noise characteristics, particularly at low injection levels. We show that the intensity fluctuation of the output light from an LED can be squeezed below the full shot-noise (FSN) level in a wide frequency range up to 800 MHz at room temperature. Such a squeezing bandwidth, three orders of magnitude wider than that in the first report on shot-noise suppression in a LED and rather close to the widest bandwidth (1.1 GHz) obtained with LDs at 77 K has been believed to be impossible. In addition, use of a separate confinement hetero(SCH-) structure in the active region allowed us to use a moderate doping concentration (5 /spl times/ 10/sup 18/ cm/sup -3/), resulting in a sufficiently high internal quantum efficiency, /spl sim/30%.

关键词： Light emitting diodes Optical noise Bandwidth Diode lasers Stimulated emission Optical devices Noise level Fluctuations Frequency Temperature distribution

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NMR Evidence for Coexistence of Superconductivity and Ferromagnetic Component in Magnetic Superconductor RuSr2YCu2O8: R99,101u and C63u NMR

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Physical Review Letters 2001年第25期86卷 5767-5767页

作者： Y. Tokunaga H. Kotegawa K. Ishida Y. Kitaoka H. Takagiwa J. Akimitsu Department of Physical Science Graduate School of Engineering Science Osaka University Toyonaka Osaka 560-8531 Japan Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation (JST) Department of Physics Aoyama-Gakuin University Setagaya-ku Tokyo 157-8572 Japan

From Ru- and Cu-NMR studies, we present evidence for coexistence of superconductivity and ferromagnetism in a cuprate superconductor RuSr2YCu2O8 (RuY1212). The observation of a large enhancement of a radio-frequency field for the Ru-NMR signal at zero field reveals the existence of a ferromagnetic (FM) component in the ordered RuO2 plane below a Curie temperature of TM=150K. Just below the onset temperature of superconductivity Tconset=45K, a remarkable decrease of the nuclear spin-lattice relaxation rate 1/T1 was observed within the ordered RuO2 plane as well as the CuO2 plane, revealing that the superconducting gap coexists with the FM component in the RuO2 plane on a microscopic scale. In addition, from the observation of a sharp peak in 101(1/T1) at Tczero∼23K where the resistivity becomes zero, we suggest that the motion of self-induced vortices originating from fluctuations of the FM component induces the resistivity between Tconset and Tczero in RuY1212.

关键词： Superconducting materials

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Evidence for Strong-Coupling s-Wave Superconductivity in MgB2: B11 NMR Study

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Physical Review Letters 2001年第12期87卷 127001-127001页

作者： H. Kotegawa K. Ishida Y. Kitaoka T. Muranaka J. Akimitsu Department of Physical Science Graduate School of Engineering Science Osaka University Toyonaka Osaka 560-8531 Japan Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation (JST) Kawaguchi Saitama 332-0012 Japan Department of Physics Aoyama-Gakuin University Setagaya-ku Tokyo 157-8572 Japan

We have investigated a gap structure in a newly discovered superconductor, MgB2, through measurement of the 11B nuclear spin-lattice relaxation rate, 11(1/T1). 11(1/T1) is proportional to the temperature (T) in the normal state, and decreases exponentially in the superconducting (SC) state, revealing a tiny coherence peak just below Tc. The T dependence of 1/T1 in the SC state can be accounted for by an s-wave SC model with a large gap size of 2Δ/kBTc∼5 which suggests it is in a strong-coupling regime.

关键词： Superconducting materials

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Mssbauer Study of ε-Fe under External Magnetic Field

Mssbauer Study of ε-Fe under External Magnetic Field

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18th International Conference on High Pressure science and technology

作者： Saburo Nasu Tetsuya Sasaki Takateru Kawakami Toshio Tsutsui Shoichi Endo University Toyonaka Osaka 560-8531 Japan Research Center for Material Science at Extreme Conditions Osaka University Toyonaka Osaka 560-8531 Japan Core Research for Evolutional Science and Technology (CREST Research Center for Material Science at Extreme Conditions Osaka University Toyonaka Osaka 560-8531 Japan Core Research for Evolutional Science and Technology (CREST University Toyonaka Osaka 560-8531 Japan University Toyonaka Osaka 560-8531 Japan

Using a diamond anvil cell, the 57Fe Mossbauer measurements of high-pressure phase of iron, -Fe at 20 GPa, have been performed at 4.5 K under external magnetic fields up to 7 T. Magnitude of the hyperfine magnetic fields depends linearly on the external magnetic fields, Hext. It implies that there is no induced hyperfine field due to the local magnetic and -Fe under 20 GPa at 4.5 K is determined as a Pauli paramagnet. It is well recognized that the high-pressure phase of iron, -Fe, does not show any magnetic ordere down to 30 mK [1]. Whether the Fe atoms in -Fe have a local moment showing a magnetic order below 30 mK or Fe has no magnetic moment at all is important question, because the non-magnetic Fe might show the superconductivity [2]. In this investigation, we performed again the 57Fe Mossbauer measurements of -Fe at 20 GPa under externally applied magnetic fields up to 7 T at 4.5 K in order to detect the existence or non-existence of the local magnetic moment of Fe in -Fe. Basset type diamond anvil cell (DAC) made of Cu-Be alloy was used. 975 MBq 57Co in Rh matrix and 95.5% 57Fe foil were used as an -ray source and an absorber specimen. Typical 57Fe Mossbauer spectra obtained from -Fe at 4.5 K under longitudinally applied magnetic fields up to 7 T were shown in Fig. 1. High magnetic fields were supplied by using a superconducting magnet on the absorber specimen and also on the -ray source 57Co in Rh. Induced hyperfine fields at 57Fe in Rh source at 4.5 K were determined as a function of Hext by the measurements using a Pd-2%Fe single line absorber placed outside of the cryostat. Using these values, the magntitude of the field at 57Fe nucleus in -Fe was determined and the observed magnetic field depends linearly on the external magnetic field. From the results obtained it was concluded the e-Fe at 4.5 K under 20 GPa is Pauli paramagnet.

关键词： High Pressure Mossbauer, DAC, Fe

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Dielectric and magnetic anomalies and spin frustration in hexagonal RMnO3 (R=Y, Yb, and Lu)

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Physical Review B 2001年第10期64卷 104419-104419页

作者： T. Katsufuji S. Mori M. Masaki Y. Moritomo N. Yamamoto H. Takagi Department of Advanced Materials Science and Department of Applied Chemistry University of Tokyo Tokyo 113-8656 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Corporation Japan Department of Physics Tokyo Institute of Technology Tokyo 152-8551 Japan CIRSE and Department of Crystalline Materials Science Nagoya University Nagoya 464-8601 Japan

Single crystals of hexagonal RMnO3 (R=Y, Yb, and Lu), where Mn ions form the triangular lattice, were investigated, focusing on their dielectric/magnetic anomalies as well as geometrical spin frustration. It is found that the ratio of a Weiss temperature to TN is ∼10 in RMnO3, indicating the dominant role of strong geometrical frustration. The effect of geometrical frustration also appears in specific heat, which shows a presence of a substantial amount of residual magnetic contribution below TN, indicating that a part of the spins are still fluctuating at T≪TN. It is also found that the dielectric anomaly at TN is strongly anisotropic, suggesting a unique correlation between magnetism and dielectric properties in these compounds.

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