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Search Results: 1 - 10 of 86 matches for " Kentarou Sawano "
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TEM Observation of Si0.99C0.01 Thin Films with Arsenic-Ion-, Boron-Ion-, and Silicon-Ion-Implantation Followed by Rapid Thermal Annealing  [PDF]
Junji Yamanaka, Shigenori Inoue, Keisuke Arimoto, Kiyokazu Nakagawa, Kentarou Sawano, Yasuhiro Shiraki, Atsushi Moriya, Yasuhiro Inokuchi, Yasuo Kunii
Journal of Materials Science and Chemical Engineering (MSCE) , 2017, DOI: 10.4236/msce.2017.51003
Abstract:
Strained Si and its related materials, such as strained SiGe and strained silicon-carbon alloy (Si-C), are receiving tremendous interest due to their high carrier mobility. In this study we carry out a basic investigation of the change in microstructure of ion-implanted Si-C solid solution caused by rapid thermal annealing, because it is very important to realize a field-effect transistor made of this new material. The microstructures of arsenic-ion-, boron-ion-, and silicon-ion-implanted Si0.99C0.01 specimens upon thermal annealing are observed using transmission electron microscopy, and it is revealed that the rate of solid-state crystallization of ion-implanted Si-C is slower than that of the ion-implanted Si.
Electronic Transport Properties of the Ising Quantum Hall Ferromagnet in a Si Quantum Well
Kiyohiko Toyama,Takahisa Nishioka,Kentarou Sawano,Yasuhiro Shiraki,Tohru Okamoto
Physics , 2008, DOI: 10.1103/PhysRevLett.101.016805
Abstract: Magnetotransport properties are investigated for a high mobility Si two dimensional electron systems in the vicinity of a Landau level crossing point. At low temperatures, the resistance peak having a strong anisotropy shows large hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak is split into two peaks in the paramagnetic regime. A mean field calculation for the peak positions indicates that electron scattering is strong when the pseudospin is partially polarized. We also study the current-voltage characteristics which exhibit a wide voltage plateau.
In-plane magnetic field dependence of cyclotron relaxation time in a Si two-dimensional electron system
Tasuku Chiba,Ryuichi Masutomi,Kentarou Sawano,Yasuhiro Shiraki,Tohru Okamoto
Physics , 2013, DOI: 10.1103/PhysRevB.86.045310
Abstract: Cyclotron resonance of two-dimensional electrons is studied for a high-mobility Si/SiGe quantum well in the presence of an in-plane magnetic field, which induces spin polarization. The relaxation time $\tau_{CR}$ shows a negative in-plane magnetic field dependence, which is similar to that of the transport scattering time $\tau_t$ obtained from dc resistivity. The resonance magnetic field shows an unexpected negative shift with increasing in-plane magnetic field.
Well-width dependence of valley splitting in Si/SiGe quantum wells
Kohei Sasaki,Ryuichi Masutomi,Kiyohiko Toyama,Kentarou Sawano,Yasuhiro Shiraki,Tohru Okamoto
Physics , 2009, DOI: 10.1063/1.3270539
Abstract: The valley splitting in Si two-dimensional electron systems is studied using Si/SiGe single quantum wells (QWs) with different well widths. The energy gaps for 4 and 5.3 nm QWs, obtained from the temperature dependence of the longitudinal resistivity at the Landau level filling factor $\nu=1$, are much larger than those for 10 and 20 nm QWs. This is consistent with the well-width dependence of the bare valley splitting estimated from the comparison with the Zeeman splitting in the Shubnikov-de Haas oscillations.
Insulating Phases Induced by Crossing of Partially Filled Landau Levels in a Si Quantum Well
Tohru Okamoto,Kohei Sasaki,Kiyohiko Toyama,Ryuichi Masutomi,Kentarou Sawano,Yasuhiro Shiraki
Physics , 2009, DOI: 10.1103/PhysRevB.79.241302
Abstract: We study magnetotransport in a high mobility Si two-dimensional electron system by in situ tilting of the sample relative to the magnetic field. A pronounced dip in the longitudinal resistivity is observed during the Landau level crossing process for noninteger filling factors. Together with a Hall resistivity change which exhibits the particle-hole symmetry, this indicates that electrons or holes in the relevant Landau levels become localized at the coincidence where the pseudospin-unpolarized state is expected to be stable.
Metallic Behavior of Cyclotron Relaxation Time in Two-Dimensional Systems
Ryuichi Masutomi,Kohei Sasaki,Ippei Yasuda,Akihito Sekine,Kentarou Sawano,Yasuhiro Shiraki,Tohru Okamoto
Physics , 2011, DOI: 10.1103/PhysRevLett.106.196404
Abstract: Cyclotron resonance of two-dimensional electrons is studied at low temperatures down to 0.4 K for a high-mobility Si/SiGe quantum well which exhibits a metallic temperature dependence of dc resistivity $\rho$. The relaxation time $\tau_{\rm CR}$ shows a negative temperature dependence, which is similar to that of the transport scattering time $\tau_t$ obtained from $\rho$. The ratio $\tau_{\rm CR}/\tau_t$ at 0.4 K increases as the electron density $N_s$ decreases, and exceeds unity when $N_s$ approaches the critical density for the metal-insulator transition.
Excitonic Aharonov-Bohm Effect in Isotopically Pure 70Ge/Si Type-II Quantum Dots
Satoru Miyamoto,Oussama Moutanabbir,Toyofumi Ishikawa,Mikio Eto,Eugene E. Haller,Kentarou Sawano,Yasuhiro Shiraki,Kohei M. Itoh
Physics , 2010, DOI: 10.1103/PhysRevB.82.073306
Abstract: We report on a magneto-photoluminescence study of isotopically pure 70Ge/Si self-assembled type-II quantum dots. Oscillatory behaviors attributed to the Aharonov-Bohm effect are simultaneously observed for the emission energy and intensity of excitons subject to an increasing magnetic field. When the magnetic flux penetrates through the ring-like trajectory of an electron moving around each quantum dot, the ground state of an exciton experiences a change in its angular momentum. Our results provide the experimental evidence for the phase coherence of a localized electron wave function in group-IV Ge/Si self-assembled quantum structures.
Exchange-driven magnetoresistance in silicon facilitated by electrical spin injection
Yuichiro Ando,Lan Qing,Yang Song,Shinya Yamada,Kenji Kasahara,Kentarou Sawano,Masanobu Miyao,Hanan Dery,Kohei Hamaya
Physics , 2014,
Abstract: We use electrical spin injection to probe exchange interactions in phosphorus doped silicon (Si:P). The detection is enabled by a magnetoresistance effect that demonstrates the efficiency of exchange in imprinting spin information from the magnetic lead onto the localized moments in the Si:P region. A unique Lorentzian-shaped signal existing only at low temperatures ($\lesssim 25 K$) is observed experimentally and analyzed theoretically in electrical Hanle effect measurement. It stems from spin-dependent scattering of electrons by neutral impurities in Si:P. The shape of this signal is not directly related to spin relaxation but to exchange interaction between spin-polarized electrons that are localized on adjacent impurities.
Cubic Rashba spin-orbit interaction of two-dimensional hole gas in strained-Ge/SiGe quantum well
Rai Moriya,Kentarou Sawano,Yusuke Hoshi,Satoru Masubuchi,Yasuhiro Shiraki,Andreas Wild,Christian Neumann,Gerhard Abstreiter,Dominique Bougeard,Takaaki Koga,Tomoki Machida
Physics , 2014, DOI: 10.1103/PhysRevLett.113.086601
Abstract: The spin-orbit interaction (SOI) of the two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-Ge/SiGe quantum well structure. We observed weak anti-localization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the k-cubic Rashba SOI theory. Furthermore, we demonstrated electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained-Ge is a purely cubic-Rashba-system, which is consistent with the spin angular momentum mj = +-3/2 nature of the HH wave function.
Tau polarization in SUSY cascade decays at LHC
Mawatari, Kentarou
High Energy Physics - Phenomenology , 2007,
Abstract: We explore how the polarization of the tau leptons in the cascade decay $\tilde{q}\to q\tilde\chi^0_2\to q\tau\tilde\tau\to q\tau\tau\tilde\chi^0_1$ can be exploited to study mixing properties of neutralinos and staus. We present details of the analysis including experimental effects such as transverse momentum cuts for the $\tau\to\pi\nu$ decay mode, and show that the di-pion invariant mass distribution provides valuable information on their properties.
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