Results for "Takashi Taniguchi"

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Distributions of discriminants of cubic algebras IIAug 26 2006Let $k$ be a number field and $O$ the ring of integers. In the previous paper [T06] we study the Dirichlet series counting discriminants of cubic algebras of $O$ and derive some density theorems on distributions of the discriminants by using the theory ... More
Distributions of discriminants of cubic algebrasJun 05 2006We study the space of binary cubic and quadratic forms over the ring of integers $O$ of an algebraic number field $k$. By applying the theory of prehomogeneous vector spaces founded by M. Sato and T. Shintani, we can associate the zeta functions for these ... More
On proportional constants of the mean value of class numbers of quadratic extensionsOct 04 2004In this article, we slightly refine the mean value theorem for the class number of quadratic extensions obtained by Goldfeld-Hoffstein and Datskovsky. We determine all the proportional constants of the mean value with respect to the local conditions including ... More
Anisotropic Dielectric Breakdown Strength of Single Crystal Hexagonal Boron NitrideOct 31 2016Dielectric breakdown has historically been of great interest from the perspectives of fundamental physics and electrical reliability. However, to date, the anisotropy in the dielectric breakdown has not been discussed. Here, we report an anisotropic dielectric ... More
On parameterizations of rational orbits of some forms of prehomogeneous vector spacesAug 26 2006In this paper, we consider the structure of rational orbit of some prehomogeneous vector spaces originally motivated by Wright and Yukie. After we give a refinement of Wright-Yukie's construction, we apply it to the inner forms of the $D_5$ and $E_7$ ... More
A mean value theorem for orders of degree zero divisor class groups of quadratic extensions over a function fieldMar 14 2002Let $k$ be a function field of one variable over a finite field with the characteristic not equal to two. In this paper, we consider the prehomogeneous representation of the space of binary quadratic forms over $k$. We have two main results. The first ... More
(2+1)-flavor QCD Thermodynamics from the Gradient FlowNov 10 2015Recently, we proposed a novel method to define and calculate the energy-momentum tensor (EMT) in lattice gauge theory on the basis of the Yang-Mills gradient flow [1]. In this proceedings, we summarize the basic idea and technical steps to obtain the ... More
Dry transfer of CVD graphene using MoS$_2$-based stampsJun 01 2017Recently, a contamination-free dry transfer method for graphene grown by chemical vapor deposition (CVD) has been reported that allows to directly pick-up graphene from the copper growth substrate using a flake of hexagonal boron nitride (hBN), resulting ... More
A mean value theorem for the square of class number times regulator of quadratic extensionsOct 25 2004Jul 03 2006Let $k$ be a number field. In this paper, we give a formula for the mean value of the square of class numbers times regulators for certain families of quadratic extensions of $k$ characterized by finitely many local conditions. We approach this by using ... More
On the zeta functions of prehomogeneous vector spaces for pair of simple algebrasMar 16 2004In this paper, we consider the prehomogeneous vector space for pair of simple algebras which are $k$-forms of the $D_4$ type and the $E_6$ type. We mainly study the non-split cases. The main purpose of this paper is to determine the principal parts of ... More
Multiscale Simulation of History Dependent Flow in Polymer MeltDec 14 2010Mar 09 2011We have developed a new multiscale simulation technique to investigate history-dependent flow behavior of entangled polymer melt, using a smoothed particle hydrodynamics simulation with microscopic simulators that account for the dynamics of entangled ... More
An error estimate for counting $S_3$-sextic number fieldsAug 10 2012Oct 01 2013In this note, we prove a power-saving remainder term for the function counting $S_3$-sextic number fields. We also give a prediction on the second main term. We also present numerical data on counting functions for $S_3$-sextic number fields. Our data ... More
Equilibrium sequences of irrotational binary polytropic stars : The case of double polytropic starsApr 03 2000Solutions to equilibrium sequences of irrotational binary polytropic stars in Newtonian gravity are expanded in a power of $\epsilon=a_0/R$, where R and $a_0$ are the orbital separation of the binary system and the radius of each star for $R=\infty$. ... More
BN/Graphene/BN Transistors for RF ApplicationsAug 09 2011In this letter, we demonstrate the first BN/Graphene/BN field effect transistor for RF applications. The BN/Graphene/BN structure can preserve the high mobility of graphene, even when it is sandwiched between a substrate and a gate dielectric. Field effect ... More
Nf=2+1 QCD thermodynamics from gradient flowSep 06 2016The energy-momentum tensor is a very important quantity in QCD thermodynamics. Its expectation value contains information of the pressure and the energy density as its diagonal part. Further properties like viscosity and specific heat can be extracted ... More
Robust nonabelian ground states and continuous quantum phase transitions in a half filled bilayer graphene Landau levelNov 22 2016In a topological quantum bit, quantum information is protected from decoherence by the energy gap separating the nonabelian vacuum from higher energy modes. Experimental systems predicted to harbor nonabelions range from p-wave superfluids to superconducting ... More
Ballistic transport exceeding 28 μm in CVD grown grapheneNov 27 2015Jan 12 2016We report on ballistic transport over more than 28 \mu m in graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride. The structures are fabricated by an advanced dry van-der-Waals transfer method and exhibit ... More
Why Does NGC 1068 Have a More Powerful Active Galactic Nucleus than NGC 4258 ?May 12 1997The nuclear gas kinematics probed by water vapor maser emission has shown that two nearby active galaxies, NGC 1068 and NGC 4258, have a supermassive object in their nuclei and their masses are nearly comparable; a few 10^7 solar masses. Nevertheless, ... More
Dusty Tori of Seyfert Nuclei Probed by the Water Vapor Maser Emission: How Large are the Dusty Tori ?May 08 1998Geometrical and physical properties of dusty tori of Seyfert nuclei probed by the water vapor maser emission at 22 GHz are discussed. We assume that the dusty torus has a simple cylindrical form and the maser emission can be detected only when we observe ... More
Flow-History-Dependent Behavior in Entangled Polymer Melt Flow with Multiscale SimulationOct 05 2011Polymer melts represent the flow-history-dependent behavior. To clearly show this behavior, we have investigated flow behavior of an entangled polymer melt around two cylinders placed in tandem along the flow direction in a two dimensional periodic system. ... More
Secondary terms in counting functions for cubic fieldsFeb 14 2011We prove the existence of secondary terms of order X^{5/6} in the Davenport-Heilbronn theorems on cubic fields and 3-torsion in class groups of quadratic fields. For cubic fields this confirms a conjecture of Datskovsky-Wright and Roberts. We also prove ... More
Multiscale Lagrangian Fluid Dynamics Simulation for Polymeric FluidMay 13 2009Dec 10 2009We have developed a simulation technique of multiscale Lagrangian fluid dynamics to tackle hierarchical problems relating to historical dependency of polymeric fluid. We investigate flow dynamics of dilute polymeric fluid by using the multiscale simulation ... More
High-quality dry transferred CVD bilayer grapheneApr 14 2017We report on the fabrication and characterization of high-quality chemical vapor-deposited (CVD) bilayer graphene (BLG). In particular, we demonstrate that CVD-grown BLG can mechanically be detached from the copper foil by an hexagonal boron nitride (hBN) ... More
Where is the coronal line region in active galactic nuclei?Feb 11 1998We report the new finding that type 1 Seyfert nuclei (S1s) have excess [FeVII]6087 emission with respect to type 2s (S2s). The S1s exhibit broad emission lines which are attributed to ionized gas within 1 pc of the black hole, whereas the S2s do not show ... More
Relations among Dirichlet series whose coefficients are class numbers of binary cubic forms IIDec 21 2011As a continuation of the authors and Wakatsuki's previous paper [5], we study relations among Dirichlet series whose coefficients are class numbers of binary cubic forms. We show that for any integral models of the space of binary cubic forms, the associated ... More
Tunneling transport in a few monolayer-thick WS2/graphene heterojunctionNov 18 2014Dec 09 2014This paper demonstrates the high-quality tunnel barrier characteristics and layer number controlled tunnel resistance of a transition metal dichalcogenide (TMD) measuring just a few monolayers in thickness. Investigation of vertical transport in WS2 and ... More
Giant Frictional Drag in Double Bilayer Graphene HeterostructuresMar 02 2016We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2 $-$ 5 nm thick hexagonal boron nitride dielectric. At temperatures ($T$) lower than $\sim$ 10 K, we observe a large anomalous negative drag emerging predominantly ... More
Dry-transferred CVD graphene for inverted spin valve devicesSep 05 2017Integrating high-mobility graphene grown by chemical vapor deposition (CVD) into spin transport devices is one of the key tasks in graphene spintronics. We use a van der Waals pickup technique to transfer CVD graphene by hexagonal boron nitride (hBN) ... More
A New Dual-Component Photoionization Model for the Narrow Emission-Line Regions in Active Galactic NucleiJun 22 1998Having found that type 1 Seyfert nuclei have excess [FeVII]6087 emission with respect to type 2s, Murayama & Taniguchi have proposed that the high-ionization nuclear emission-line region (HINER) traced by the [FeVII]6087 emission resides in the inner ... More
Almost analytic solutions to equilibrium sequences of irrotational binary polytropic stars for n=1Nov 23 1999A solution to an equilibrium of irrotational binary polytropic stars in Newtonian gravity is expanded in a power of \epsilon=a_0/R, where R and a_0 are the separation of the binary system and the radius of each star for R=\infty. For the polytropic index ... More
Temperature dependence of topological susceptibility using gradient flowNov 08 2016We study temperature dependence of the topological susceptibility with the $N_{f}=2+1$ flavors Wilson fermion. We have two major interests in this paper. One is a comparison of gluonic and fermionic definitions of the topological susceptibility. Two definitions ... More
Star-Forming Galaxies at z=0.24 in the Subaru Deep Field and the Sloan Digital Sky SurveyJul 01 2008We make a search for Halpha emitting galaxies at z=0.24 in the Subaru Deep Field (SDF) using the archival data set obtained with the Subaru Telescope. We carefully select Halpha emitters in the narrowband filter NB816, using B, V, Rc, i', and z' broad-band ... More
Absorptive pinhole collimators for ballistic Dirac fermions in grapheneNov 16 2016Nov 17 2016Ballistic electrons in solids can have mean free paths far larger than the smallest features patterned by lithography. This has allowed development and study of solid-state electron-optical devices such as beam splitters and quantum point contacts, which ... More
Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene spin-valves with atomic layer deposited Al$_2$O$_3$ spin injection and detection barriersJul 09 2015We present spin transport studies on bi- and trilayer graphene non-local spin-valves which have been fabricated by a bottom-up fabrication method. By this technique, spin injection electrodes are first deposited onto Si$^{++}$/SiO$_2$ substrates with ... More
From diffusive to ballistic transport in etched graphene constrictions and nanoribbonsJun 29 2017Graphene nanoribbons and constrictions are envisaged as fundamental components of future carbon-based nanoelectronic and spintronic devices. At nanoscale, electronic effects in these devices depend heavily on the dimensions of the active channel and the ... More
Aharonov-Bohm oscillations and magnetic focusing in ballistic graphene ringsSep 02 2017We present low-temperature magnetotransport measurements on graphene rings encapsulated in hexagonal boron nitride. We investigate phase-coherent transport and show Aharonov-Bohm (AB) oscillations in quasi-ballistic graphene rings with hard confinement. ... More
LRG J0239-0134: A Ring Galaxy or a Pair of Superbubbles at z=1 ?Nov 03 2000The unusual morphology of LRG J0239$-$0134 at $z$ =1.062 has been interpreted as a ring galaxy. Here we propose an alternative idea that the ring-like morphology is attributed to a pair of superbubbles driven by the intense starburst in the central region ... More
Innermost Stable Circular Orbit of Coalescing Neutron Star-Black Hole Binary --- Generalized Pseudo-Newtonian Potential Approach ---Sep 02 1996The innermost stable circular orbits (ISCO) of coalescing neutron star-black hole binary are studied taking into account both the tidal and relativistic effects. We adopt the generalized pseudo-Newtonian potential to mimic the general relativistic effects ... More
Orbital exponential sums for prehomogeneous vector spacesJul 26 2016Let (G, V) be a prehomogeneous vector space, let O be any G(F_q)-invariant subset of V(F_q), and let f be the characteristic function of O. In this paper we develop a method for explicitly and efficiently evaluating the Fourier transform of f, based on ... More
Orbital L-functions for the space of binary cubic formsDec 21 2011We introduce the notion of orbital L-functions for the space of binary cubic forms and investigate their analytic properties. We study their functional equations and residue formulas in some detail. Aside from the intrinsic interest, results from this ... More
Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer GrapheneOct 20 2011We investigate electronic transport in dual-gated twisted bilayer graphene. Despite the sub-nanometer proximity between the layers, we identify independent contributions to the magnetoresistance from the graphene Landau level spectrum of each layer. We ... More
Equation of state in (2+1)-flavor QCD with gradient flowOct 29 2016The energy-momentum tensor and equation of state are studied in finite-temperature (2+1)-flavor QCD with improved Wilson quarks using the method proposed by Makino and Suzuki based on the gradient flow. We find that the results of the gradient flow are ... More
Shubnikov-de Haas oscillations of high mobility holes in monolayer and bilayer WSe$_2$: Landau level degeneracy, effective mass, and negative compressibilityFeb 02 2016We study the magnetotransport properties of high mobility holes in monolayer and bilayer WSe$_2$, which display well defined Shubnikov-de Haas (SdH) oscillations, and quantum Hall states (QHSs) in high magnetic fields. In both mono and bilayer WSe$_2$, ... More
Tunneling in graphene-topological insulator hybrid devicesApr 30 2015Hybrid graphene-topological insulator (TI) devices were fabricated using a mechanical transfer method and studied via electronic transport. Devices consisting of bilayer graphene (BLG) under the TI Bi$_2$Se$_3$ exhibit differential conductance characteristics ... More
Boron Nitride Nanosheets as Improved and Reusable Substrates for Gold Nanoparticles Enabled Surface Enhanced Raman SpectroscopyMar 11 2015Atomically thin boron nitride (BN) nanosheets have been found an excellent substrate for noble metal particles enabled surface enhanced Raman spectroscopy (SERS), thanks to their good adsorption of aromatic molecules, high thermal stability and weak Raman ... More
Nanosecond spin lifetimes in single- and few-layer graphene-hBN heterostructures at room temperatureJun 10 2014We present a new fabrication method of graphene spin-valve devices which yields enhanced spin and charge transport properties by improving both the electrode-to-graphene and graphene-to-substrate interface. First, we prepare Co/MgO spin injection electrodes ... More
Disorder From the Bulk Ionic Liquid in Electric Double Layer TransistorsJan 23 2018Ionic liquid gating has a number of advantages over solid-state gating, especially for flexible or transparent devices and for applications requiring high carrier densities. However, the large number of charged ions near the channel inevitably results ... More
Probing electronic lifetimes and phonon anharmonicities in high-quality chemical vapor deposited graphene by magneto-Raman spectroscopyNov 29 2015We present a magneto-Raman study on high-quality single-layer graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride by a dry transfer technique. By analyzing the Raman D, G, and 2D peaks, we find that ... More
Electrical spin injection into graphene through monolayer hexagonal boron nitrideMay 30 2013We demonstrate electrical spin injection from a ferromagnet to a bilayer graphene (BLG) through a monolayer (ML) of single-crystal hexagonal boron nitride (h-BN). A Ni81Fe19/ML h-BN/BLG/h-BN structure is fabricated using a micromechanical cleavage and ... More
A high-mobility electronic system at an electrolyte-gated oxide surfaceOct 11 2014Electrolyte gating is a powerful technique for accumulating large carrier densities in surface two-dimensional electron systems (2DES). Yet this approach suffers from significant sources of disorder: electrochemical reactions can damage or alter the surface ... More
Chemical Potential and Quantum Hall Ferromagnetism in Bilayer GrapheneJan 03 2014Jul 07 2014Bilayer graphene has a unique electronic structure influenced by a complex interplay between various degrees of freedom. We probe its chemical potential using double bilayer graphene heterostructures, separated by a hexagonal boron nitride dielectric. ... More
Exciton energy-momentum map of hexagonal boron nitrideAug 07 2015Understanding and controlling the way excitons propagate in solids is a key for tailoring materials with improved optoelectronic properties. A fundamental step in this direction is the determination of the exciton energy-momentum dispersion. Here, thanks ... More
Band gap and broken chirality in single-layer and bilayer grapheneAug 11 2015Aug 21 2015Chirality is one of the key features governing the electronic properties of single- and bilayer graphene: the basics of this concept and its consequences on transport are presented in this review. By breaking the inversion symmetry, a band gap can be ... More
Line Shape of the Raman 2D Peak of Graphene in Van Der Waals HeterostructuresAug 09 2016The Raman 2D line of graphene is widely used for device characterization and during device fabrication as it contains valuable information on e.g. the direction and magnitude of mechanical strain and doping. Here we present systematic asymmetries in the ... More
Spatial control of laser-induced doping profiles in graphene on hexagonal boron nitrideNov 02 2015We present a method to create and erase spatially resolved doping profiles in graphene-hexagonal boron nitride (hBN) heterostructures. The technique is based on photo-induced doping by a focused laser and does neither require masks nor photo resists. ... More
Quantum transport through MoS$_2$ constrictions defined by photodopingDec 04 2016We present a device scheme to explore mesoscopic transport through molybdenum disulfide (MoS$_2$) constrictions using photodoping. The devices are based on van-der-Waals heterostructures where few-layer MoS$_2$ flakes are partially encapsulated by hexagonal ... More
Identifying suitable substrates for high-quality graphene-based heterostructuresOct 27 2016We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphene-based heterostuctures on a large number of different substrate materials, ... More
Spin lifetimes exceeding 12 nanoseconds in graphene non-local spin valve devicesFeb 08 2016We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5 \mu m in single layer graphene non-local spin transport devices at room temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a Si/SiO$_2$ substrate and ... More
Low B Field Magneto-Phonon Resonances in Single-Layer and Bilayer GrapheneApr 14 2015Apr 16 2015Many-body effects resulting from strong electron-electron and electron-phonon interactions play a significant role in graphene physics. We report on their manifestation in low B field magneto-phonon resonances in high quality exfoliated single-layer and ... More
Electrical generation and detection of spin waves in a quantum Hall ferromagnetJan 25 2018Spin waves are essential to understanding the intrinsic ordering and thermodynamic properties of magnetic systems. An attractive candidate for studying long-lived spin-wave physics is the quantum Hall (QH) ferromagnet, which forms spontaneously in clean ... More
Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2/Gr/hBN heterostructuresDec 15 2017Dec 18 2017Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit ... More
Subaru Spectropolarimetry of Mrk 573: The Hidden High-Ionization Nuclear Emission-Line Region inside the Dusty TorusAug 13 2004We report on the result of our high quality spectropolarimetric observation for the narrow-line region in a nearby Seyfert 2 galaxy, Mrk 573, by the Subaru Telescope. The polarized flux spectrum of Mrk 573 shows not only prominent scattered broad H$\alpha$ ... More
Photo-thermionic effect in vertical graphene heterostructuresJan 16 2016Jun 10 2016Finding alternative optoelectronic mechanisms that overcome the limitations of conventional semiconductor devices is paramount for detecting and harvesting low-energy photons. A highly promising approach is to drive a current from the thermal energy added ... More
Evidence for a Spin Phase Transition at ν=0 in Bilayer GrapheneDec 16 2012Feb 16 2013The most celebrated property of the quantum spin Hall effect is the presence of spin-polarized counter-propagating edge states. This novel edge state configuration has also been predicted to occur in graphene when spin-split electron- and hole-like Landau ... More
Electrical characterization of fully encapsulated ultra thin black phosphorus-based heterostructures with graphene contactsDec 03 2014The presence of finite bandgap and high mobility in semiconductor few-layer black phosphorus offers an attractive prospect for using this material in future two-dimensional electronic devices. Here we demonstrate for the first time fully encapsulated ... More
Seyfert-Type Dependences of Narrow Emission-Line Ratios and Physical Properties of High-Ionization Nuclear Emission-Line Regions in Seyfert GalaxiesJul 02 2001In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission ... More
Dusty Tori of Seyfert NucleiJan 26 2000Dusty tori around active galactic nuclei (AGNs) play an important role in the classification of Seyfert galaxies. Therefore, physical properties of dusty tori are of great interest. We briefly introduce three statistical studies investigating properties ... More
Multiscale simulation of polymer melt spinning by using the dumbbell modelSep 03 2016We investigated the spinning process of a polymeric material by using a multiscale simulation method which connects the macroscopic and microscopic states through the stress and strain-rate tensor fields, by using Lagrangian particles (filled with polymer ... More
Unconventional Correlation between Quantum Hall Transport Quantization and Bulk State Filling in Gated Graphene DevicesNov 04 2015Oct 28 2016We report simultaneous transport and scanning microwave impedance microscopy to examine the correlation between transport quantization and filling of the bulk Landau levels in the quantum Hall regime in gated graphene devices. Surprisingly, a comparison ... More
Spatially resolved edge currents and guided-wave electronic states in grapheneApr 28 2015A far-reaching goal of graphene research is exploiting the unique properties of carriers to realize extreme nonclassical electronic transport. Of particular interest is harnessing wavelike carriers to guide and direct them on submicron scales, similar ... More
Band Structure Mapping of Bilayer Graphene via Quasiparticle ScatteringJun 03 2014A perpendicular electric field breaks the layer symmetry of Bernal-stacked bilayer graphene, resulting in the opening of a band gap and a modification of the effective mass of the charge carriers. Using scanning tunneling microscopy and spectroscopy, ... More
Thermoelectric detection of propagating plasmons in grapheneJan 08 2016Controlling, detecting and generating propagating plasmons by all-electrical means is at the heart of on-chip nano-optical processing. Graphene carries long-lived plasmons that are extremely confined and controllable by electrostatic fields, however electrical ... More
Stacking transition in bilayer graphene caused by thermally activated rotationDec 07 2016Crystallographic alignment between two-dimensional crystals in van der Waals heterostructures brought a number of profound physical phenomena, including observation of Hofstadter butterfly and topological currents, and promising novel applications, such ... More
Probing magnetism in 2D van der Waals crystalline insulators via electron tunnelingJan 26 2018Magnetic insulators are a key resource for next-generation spintronic and topological devices. The family of layered metal halides promises ultrathin insulating multiferroics, spin liquids, and ferromagnets, but new characterization methods are required ... More
Emergence of Topologically Protected Helical States in Minimally Twisted Bilayer GrapheneFeb 08 2018Bilayer graphene samples in which inversion symmetry is broken have quantum valley Hall ground states that support counterpropogating topologically protected helical (TPH) edge states localized along domain walls between AB and BA stacking regions. Moreover, ... More
Direct exciton emission from atomically thin transition metal dichalcogenide heterostructures near the lifetime limitApr 30 2017We demonstrate the reduction of the inhomogeneous linewidth of the free excitons in atomically thin transition metal dichalcogenides (TMDCs) MoSe$_{2}$, WSe$_{2}$ and MoS$_{2}$ by encapsulation within few nanometer thick hBN. Encapsulation is shown to ... More
The High-Ionization Nuclear Emission-Line Region of Seyfert GalaxiesMar 04 2000Recently Murayama & Taniguchi proposed that a significant part of the high-ionization nuclear emission-line region (HINER) in Seyfert nuclei arises from the inner wall of dusty tori because type 1 Seyfert nuclei (S1s) show the excess HINER emission with ... More
Anisotropic Etching of Graphite and Graphene in a Remote Hydrogen PlasmaMar 14 2017We investigate the etching of a pure hydrogen plasma on graphite samples and graphene flakes on SiO$_2$ and hexagonal Boron-Nitride (hBN) substrates. The pressure and distance dependence of the graphite exposure experiments reveals the existence of two ... More
Where is the [O III]4363 emitting region in active galactic nuclei?Nov 04 2000The emission-line flux ratio of [O III]4363/[O III]5007 (R_OIII)is a useful diagnostic for the ionization mechanism and physical properties of emission-line regions in active galactic nuclei (AGNs). However, it is known that simple photoionization models ... More
Location of the innermost stable circular orbit of binary neutron stars in the post Newtonian approximations of general relativityJan 05 1998In this paper, we present results obtained from our recent studies on the location of the innermost stable circular orbit (ISCO) for binary neutron stars (BNSs) in several levels of post Newtonian (PN) approximations. We reach the following conclusion ... More
High-Mobility Holes in Dual-Gated WSe$_2$ Field-Effect TransistorsSep 13 2015We demonstrate dual-gated $p$-type field-effect transistors (FETs) based on few-layer tungsten diselenide (WSe$_2$) using high work-function platinum source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A device topology with contacts ... More
Anomalous sequence of quantum Hall liquids revealing tunable Lifshitz transition in bilayer grapheneMar 13 2014Sep 30 2014Fermi surface topology plays an important role in determining the electronic properties of metals. In bulk metals, the Fermi energy is not easily tunable at the energy scale needed for reaching conditions for the Lifshitz transition - a singular point ... More
Quantum Oscillations in Black Phosphorus Two-dimensional Electron GasNov 24 2014Two-dimensional electron gases (2DEG) have been an important source of experimental discovery and conceptual development in condensed matter physics for decades. When combined with the unique electronic properties of two-dimensional (2D) crystals, rich ... More
Fabry-Pérot interference in gapped bilayer graphene with broken anti-Klein tunnelingJun 13 2014Sep 30 2014We report the experimental observation of Fabry-P\'erot (FP) interference in the conductance of a gate-defined cavity in a dual-gated bilayer graphene (BLG) device. The high quality of the BLG flake, combined with the device's electrical robustness provided ... More
Zeeman Splitting and Inverted Polarization of Biexciton Emission in Monolayer WS2Jan 28 2018We investigate the magnetic-field-induced splitting of biexcitons in monolayer WS$_2$ using polarization-resolved photoluminescence spectroscopy in out-of-plane magnetic fields up to 30 T. The observed $g$ factor of the biexciton amounts to $-3.89$, closely ... More
The [O III]4363 Emitting Region Obscured by Dusty ToriJun 17 2001The emission-line flux ratio of [O III]4363/[O III]5007 is a useful diagnostic for the ionization mechanism and physical properties of narrow-line regions in active galactic nuclei. However, it is known that simple photoionization models underpredict ... More
What Are Narrow-Line Seyfert 1 Galaxies ?: Toward A Viewing-Angle-Dependent Unified Model for Seyfert GalaxiesOct 03 1999Recently growing evidence has been accumulated that the NLS1s are viewed from nearly pole-on viewing angles. However, there has been no theoretical model which explains the following important correlations; 1) weaker optical Fe II emitters always have ... More
Tunable $Γ- K$ Valley Populations in Hole-Doped Trilayer WSe$_2$Jan 10 2018We present a combined experimental and theoretical study of valley populations in the valence bands of trilayer WSe$_2$. Shubnikov$-$de Haas oscillations show that trilayer holes populate two distinct subbands associated with the $K$ and $\Gamma$ valleys, ... More
High-redshift Ly alpha emitters with a large equivalent width: Properties of i-dropout galaxies with an NB921-band depression in the Subaru Deep FieldFeb 14 2007We report new follow-up spectroscopy of i-dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed i-dropout selection method is expected to select galaxies with large equivalent width Ly alpha emission over a ... More
Poststarburst Models of LINERsMay 16 2000Since the discovery of low-ionization nuclear emission-line regions in many galaxies (LINERs), it has been recognized that they constitute a class of active galactic nuclei (AGNs) which are thought to be powered by gas accretion onto a central, supermassive ... More
New Mid-Infrared Diagnostic of the Dusty Torus Model for Seyfert NucleiAug 24 1999We propose a new diagnostic of the ``dusty torus'' model for Seyfert nuclei. Dust grains in the torus are heated by the nuclear continuum, and reradiate mostly in the mid-infrared wavelengths. From the torus geometry, it is predicted that the emission ... More
Phase-separation transitions in asymmetric lipid bilayersApr 13 2015Morphological transitions of phase separation associated with the asymmetry of lipid composition were investigated using micrometer-sized vesicles of lipid bilayers made from a lipid mixture. The complete macro-phase-separated morphology undergoes a transition ... More
On relations among Dirichlet series whose coefficients are class numbers of binary cubic formsNov 04 2007We study the class numbers of integral binary cubic forms. For each $SL_2(Z)$ invariant lattice $L$, Shintani introduced Dirichlet series whose coefficients are the class numbers of binary cubic forms in $L$. We classify the invariant lattices, and investigate ... More
Inducing Superconducting Correlation in Quantum Hall Edge StatesSep 26 2016Sep 28 2016The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a 2-dimensional electron gas (2DEG) system. A superconductor (SC) contacting these states induces correlation of the quasi-particles in the dissipationless 1D chiral ... More
Hot Carrier-Assisted Intrinsic Photoresponse in GrapheneAug 18 2011Nov 17 2011Graphene is a new material showing high promise in optoelectronics, photonics, and energy-harvesting applications. However, the underlying physical mechanism of optoelectronic response has not been established. Here, we report on the intrinsic optoelectronic ... More
Spin and valley quantum Hall ferromagnetism in grapheneJan 19 2012In a graphene Landau level (LL), strong Coulomb interactions and the fourfold spin/valley degeneracy lead to an approximate SU(4) isospin symmetry. At partial filling, exchange interactions can spontaneously break this symmetry, manifesting as additional ... More
Raman spectroscopy as probe of nanometer-scale strain variations in grapheneJun 30 2014Mar 30 2015Confocal Raman spectroscopy is a versatile, non-invasive investigation tool and a major workhorse for graphene characterization. Here we show that the experimentally observed Raman 2D line width is a measure of nanometer-scale strain variations in graphene. ... More
Inclusive and exclusive $b\to s/dγ$Oct 03 2008Oct 09 2008In this article, I review the recent results for inclusive and exclusive measurements for $b\to s\gamma$ and $b\to d\gamma$ decays from $B$ factories Belle and Babar. I describe the measurement of branching fraction and direct CP violating asymmetry for ... More
Nonperturbative Renormalization Group Function for Quantum Hall Plateau Transitions Imposed by Global SymmetriesOct 26 1998As a unified theory of integer and fractional quantum Hall plateau transitions, a nonperturbative theory of the two-parameter scaling renormalization group function is presented. By imposing global symmetries known as ``the law of corresponding states'', ... More
Dyonic BIon black hole in string inspired modelJan 22 2001Jul 07 2001We construct static and spherically symmetric particle-like and black hole solutions with magnetic and/or electric charge in the Einstein-Born-Infeld-dilaton-axion system, which is a generalization of the Einstein-Maxwell-dilaton-axion (EMDA) system and ... More