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
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
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
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
Photo-induced anomalous Hall effect in the type-II Weyl-semimetal WTe2 at room-temperatureOct 02 2018Using Hall photovoltage measurements, we demonstrate that an anomalous Hall-voltage can be induced in few layer WTe2 under circularly polarized light illumination. By applying a bias voltage along different crystal axes, we find that the photo-induced ... 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
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
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
Control of interlayer excitons in two-dimensional van der Waals heterostructuresMar 16 2018Long-lived interlayer excitons with distinct spin-valley physics in van der Waals heterostructures based on transition metal dichalcogenides make them promising for information processing in next-generation devices. While the emission characteristics ... 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
High quality electrostatically defined hall bars in monolayer grapheneJan 04 2019Jan 22 2019Realizing graphene's promise as an atomically thin and tunable platform for fundamental studies and future applications in quantum transport requires the ability to electrostatically define the geometry of the structure and control the carrier concentration, ... More
Visualizing Strain-induced Pseudo magnetic Fields in Graphene through an hBN Magnifying GlassMar 01 2017The remarkable properties of graphene are inherent to its 2D honeycomb lattice structure. Its low dimensionality, which makes it possible to rearrange the atoms by applying an external force, offers the intriguing prospect of mechanically controlling ... More
Low energy band structure in Bernal stacked hexlayer graphene: Landau fan diagram and resistance ridgeOct 04 2018Jan 23 2019The low-energy band structure of Bernal-stacked hexlayer graphene was investigated by the measuring transport properties of high-mobility graphene samples equipped with a top and a bottom gate electrode at low temperature and in a magnetic field. By analyzing ... More
Thermal Conductivity and Phonon Transport in Suspended Few-Layer Hexagonal Boron NitrideFeb 07 2013The thermal conductivity of suspended few-layer hexagonal boron nitride (h-BN) was measured using a micro-bridge device with built-in resistance thermometers. Based on the measured thermal resistance values of 11-12 atomic layer h-BN samples with suspended ... 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
Hybridized indirect excitons in MoS2/WS2 heterobilayersDec 27 2018Ensembles of indirect or interlayer excitons (IXs) are intriguing systems to explore classical and quantum phases of interacting bosonic ensembles. IXs are composite bosons that feature enlarged lifetimes due to the reduced overlap of the electron-hole ... More
Coherent Control of Two-Dimensional ExcitonsFeb 13 2019Electric dipole radiation can be controlled by coherent optical feedback, as has previously been studied by modulating the photonic environment for point dipoles placed both in optical cavities and near metal mirrors. In experiments involving fluorescent ... 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
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
Gate-Tunable Quantum Dot in a High Quality Single Layer MoS$_{\mathrm{2}}$ Van der Waals HeterostructureJan 01 2018Mar 21 2018We have fabricated an encapsulated monolayer MoS$_{\mathrm{2}}$ device with metallic ohmic contacts through a pre-patterned hBN layer. In the bulk, we observe an electron mobility as high as 3000 cm$^{\mathrm{2}}$/Vs at a density of 7 $\times$ 10$^{\mathrm{12}}$ ... More
Strange metal in magic-angle graphene with near Planckian dissipationJan 11 2019Recent experiments on magic-angle twisted bilayer graphene have discovered correlated insulating behavior and superconductivity at a fractional filling of an isolated narrow band. In this paper we show that magic-angle bilayer graphene exhibits another ... More
Gate tunable dark trions in monolayer WSe$_2$Jan 30 2019We report the observation and gate manipulation of intrinsic dark trions in monolayer WSe$_2$. By using ultraclean WSe$_2$ devices encapsulated by boron nitride, we directly resolve the weak photoluminescence of dark trions. The dark trions can be tuned ... 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
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
Quantum confined Stark effect in a MoS$_2$ monolayer van der Waals heterostructureOct 26 2017The optics of dangling-bond-free van der Waals heterostructures containing transition metal dichalcogenides are dominated by excitons. A crucial property of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a heterostructure is ... More
Giant valley-isospin conductance oscillations in ballistic grapheneAug 31 2017At high magnetic fields the conductance of graphene is governed by the half-integer quantum Hall effect. By local electrostatic gating a \textit{p-n} junction perpendicular to the graphene edges can be formed, along which quantum Hall channels co-propagate. ... More
Electron-Hole Asymmetric Integer and Fractional Quantum Hall Effect in Bilayer GrapheneDec 25 2013The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The unique combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce ... More
Ballistic miniband conduction in a graphene superlatticeMar 03 2016Rational design of artificial lattices yields effects unavailable in simple solids, and vertical superlattices of multilayer semiconductors are already used in optical sensors and emitters. Manufacturing lateral superlattices remains a much bigger challenge, ... 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
Non-trivial quantum oscillation geometric phase shift in a trivial bandFeb 12 2019Feb 13 2019The accumulation of non-trivial geometric phases in a material's response is often a tell-tale sign of a rich underlying internal structure. Studying quantum oscillations provides one of the ways to determine these geometrical phases, such as Berry's ... 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
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
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
Edge channel confinement in a bilayer graphene $n$-$p$-$n$ quantum dotSep 04 2017Jan 17 2018We combine electrostatic and magnetic confinement to define a quantum dot in bilayer graphene. The employed geometry couples $n$-doped reservoirs to a $p$-doped dot. At magnetic field values around $B = 2~$T, Coulomb blockade is observed. This demonstrates ... 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
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
Emergence of Tertiary Dirac Points in Graphene Moiré SuperlatticesFeb 10 2017The electronic structure of a crystalline solid is largely determined by its lattice structure. Recent advances in van der Waals solids, artificial crystals with controlled stacking of two-dimensional (2D) atomic films, have enabled the creation of materials ... More
Spin and Valley States in Gate-defined Bilayer Graphene Quantum DotsMar 08 2018Aug 07 2018In bilayer graphene, electrostatic confinement can be realized by a suitable design of top and back gate electrodes. We measure electronic transport through a bilayer graphene quantum dot, which is laterally confined by gapped regions and connected to ... More
Strain-modulated Bandgap and Piezo-resistive Effect in Black Phosphorus Field-effect TransistorsJan 27 2017Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the ... 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
2D Semiconductor Nonlinear Plasmonic ModulatorsFeb 12 2019A plasmonic modulator is a device that controls the amplitude or phase of propagating plasmons. In a pure plasmonic modulator, the presence or absence of a pump plasmonic wave controls the amplitude of a probe plasmonic wave through a channel. This control ... 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
Emergent Dirac gullies and gully-symmetry breaking quantum Hall states in ABA trilayer grapheneMay 02 2018Jul 19 2018We report on quantum capacitance measurements of high quality, graphite- and hexagonal boron nitride encapsulated Bernal stacked trilayer graphene devices. At zero applied magnetic field, we observe a number of electron density- and electrical displacement-tuned ... More
Full control of quantum Hall supercurrent in a side gated graphene Josephson junctionJan 17 2019We present a study of a graphene-based Josephson junction with dedicated side gates carved from the same sheet of graphene as the junction itself. These side gates are highly efficient, and allow us to modulate carrier density along either edge of the ... More
Quantum Hall Effect in Electron-Doped Black Phosphorus Field-Effect TransistorsSep 20 2018The advent of black phosphorus field-effect transistors (FETs) has brought new possibilities in the study of two-dimensional (2D) electron systems. In a black phosphorus FET, the gate induces highly anisotropic 2D electron and hole gases. Although the ... More
Visualization and Control of Single Electron Charging in Bilayer Graphene Quantum DotsSep 13 2018Graphene p-n junctions provide an ideal platform for investigating novel behavior at the boundary between electronics and optics that arise from massless Dirac fermions, such as whispering gallery modes and Veselago lensing. Bilayer graphene also hosts ... More
Interaction Driven Quantum Hall Wedding cake-like Structures in Graphene Quantum DotsSep 29 2018Quantum-relativistic matter is ubiquitous in nature; however it is notoriously difficult to probe. The ease with which external electric and magnetic fields can be introduced in graphene opens a door to creating a table-top prototype of strongly confined ... More
Electrical 2π phase control of infrared light in a 350nm footprint using graphene plasmonsMay 29 2017Modulating the amplitude and phase of light is at the heart of many applications such as wavefront shaping, transformation optics, phased arrays, modulators and sensors. Performing this task with high efficiency and small footprint is a formidable challenge. ... 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
Cubic BN optical gap and intragap optically active defectsJun 29 2018We report a comprehensive study on the optical properties of cubic boron nitride (c-BN) and its optically active defects. Using electron energy-loss spectroscopy (EELS) within a monochromated scanning transmission electron microscope (STEM) on the highest-quality ... 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
Correlated Insulating and Superconducting States in Twisted Bilayer Graphene Below the Magic AngleFeb 13 2019The emergence of flat bands and correlated behaviors in 'magic angle' twisted bilayer graphene (tBLG) has sparked tremendous interest, though many aspects of the system are under intense debate. Here we report observation of both superconductivity and ... More
Raman Spectroscopy, Photocatalytic Degradation and Stabilization of Atomically Thin Chromium TriiodideMay 23 2018As a 2D ferromagnetic semiconductor with magnetic ordering, atomically thin chromium triiodide is the latest addition to the family of two-dimensional (2D) materials. However, realistic exploration of CrI3-based devices and heterostructures is challenging, ... More
Switchable friction enabled by nanoscale self-assembly on grapheneApr 20 2015Sep 01 2015Graphene monolayers are known to display domains of anisotropic friction with twofold symmetry and anisotropy exceeding 200 percent. This anisotropy has been thought to originate from periodic nanoscale ripples in the graphene sheet, which enhance puckering ... More
Switching of intra-orbital spin excitations in electron-doped iron pnictide superconductorsJul 26 2013Aug 02 2013We investigate the doping dependence of the magnetic excitations in two-superconducting-dome-system LaFeAsO1-xDx. Using inelastic neutron scattering, spin fluctuations at different wavenumbers were observed under both superconducting domes around x = ... More
Integration of atomically thin layers of transition metal dichalcogenides into high-Q, monolithic Bragg-cavities - an experimental platform for the enhancement of optical interaction in 2D-materialsDec 03 2018Dec 05 2018We demonstrate a new approach to integrate single layer MoSeR2R and WSeR2R flakes into monolithic all-dielectric planar high-quality micro-cavities. These distributed-Bragg-reflector (DBR) cavities may e.g. be tuned to match the exciton resonance of the ... 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
Quantum Critical Transition and Kondo Screening of Magnetic Moments in GrapheneNov 19 2017Jan 11 2018In normal metals, the magnetic moment of impurity spins disappears below a characteristic Kondo temperature, TK, where coupling with the conduction-band electrons produces an entangled state that screens the local moment. In contrast, moments embedded ... More
Observation of spin-orbit coupling induced Weyl points and topologically protected Kondo effect in a two-electron double quantum dotApr 17 2018Recent years have brought an explosion of activities in the research of topological aspects of condensed-matter systems. Topologically non-trivial phases of matter are typically accompanied by protected surface states or exotic degenerate excitations ... More